Imagine, you have 10 various versions if Windows on single machine. You need some applications to work under all OSes. For example, I use VisualStudio, Far, Archivers and MSDN. Sometimes I need PhotoShop and MS Office. I dislike the idea of installing everything 10 times. The common way is assure Drive Letter assignment to be identical under all OSes. Then copy necessary Registry keys, sometimes libraries and Environment variables.

To keep Drive Letter assignment identical across OSes it worth running each next setup.exe from previously installed OS. In this case Drive Letters will be inherited. When installing Windows from boot CD or from DOS you cannot control Drive Letter and they will be assigned in some unpredictable way. Since w2k it is not possible to change letter of so called Boot partition and System partition using Disk Administrator. Partition Magic becomes the only solution.

Notes:

• Some days ago I got to know, that Drive Letter assignment can be destroyed with DOS utility fdisk with /MBR switch (repair boot loader from MBR). Another thing I experienced was disability of system recovery with setup.exe. I ran it from NT4 with restored Drive Letters with Repair option.

• Installation order. NT family have its own boot-manager (imho it is rather good) and OS-loader. Higher versions can load lower ones. But not vice versa. In spite of this fact, os-loader is unconditionally overwritten during installation. Thus, it worth installing lower versions first: NT4, then w2k, XP, .NET. Another solution - make a copy of ntldr and ntdetect.com from root directory of boot partition, then after installation restore these files. Probably, you should also backup boot-sector. I saw .NET that could not boot after installation of XP or 2k (I don't remember exactly). Restoring ntldr and ntdetect.com didn't help.

• MS removed /MAXMEM option support from .NET ntldr. I don't know how to keep both old and new ntldrs.

• NTFS partitions must be created under higher OS (for ex. 2k or XP). In this case you will obtain NTFS of newest version. If you create the partition from NT4, it will have lover version, but later w2k or XP mark it as modified by higher version of NTFS driver. Such volume becomes inaccessible for PartitionMagic. BTW, inspite of MS claims, new NTFS volumes are readable and writable under NT4. The only exception are files with complicated inherited permissions. In practice, I saw such problem only twice, and about still some I heard from other people.

And now about moving software across OSes. In general, it would be perfectly to use Axxie's Advanced Installer, but it is not written yet. Thus, we are to do everything manually. Or use similar utility - rconf

Brief HOWTO list

• Environment Variables
• MS Visual C++ 6.0
• Borland C++Builder 6
• MSDN
• MS Office 95/97
• Photoshop 7.0
• Mozilla 1.7b+
• Putty
• Far
• TheBat!

1. Boot origin OS and save the following registry key:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
   HKEY_CURENT_USER\Environment
   

2. Remove from .REG-file the following OS- and platform-dependent values:

   ComSpec
   Cpu
   NUMBER_OF_PROCESSORS
   OS
   Os2LibPath
   PROCESSOR_ARCHITECTURE
   PROCESSOR_IDENTIFIER
   PROCESSOR_LEVEL
   PROCESSOR_REVISION
   

3. Boot target OS and load edited .REG-file.

1. Boot OS with installed VisualStudio then save the following registry keys:

   HKEY_CLASSES_ROOT\.dsp
   HKEY_CLASSES_ROOT\dspfile
   HKEY_CLASSES_ROOT\.dsw
   HKEY_CLASSES_ROOT\dswfile
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\DevStudio
   HKEY_CURRENT_USER\Software\Microsoft\VisualStudio
   HKEY_CURRENT_USER\Software\Microsoft\DevStudio
   

2. Boot OS without VisualStudio and load previously saved registry keys.
3. Copy the following files from System32 of the old Windows installation to System32 of the new installation. These are libraries, used for Debug builds.

   MFC42D.DLL	MFC42D.MAP	MFC42D.PDB
   MFC42UD.DLL	MFC42UD.MAP	MFC42UD.PDB
   MFCD42D.DLL	MFCD42D.MAP	MFCD42D.PDB
   MFCD42UD.DLL	MFCD42UD.MAP	MFCD42UD.PDB
   MFCN42D.DLL	MFCN42D.MAP	MFCN42D.PDB
   MFCN42UD.DLL	MFCN42UD.MAP	MFCN42UD.PDB
   MFCO42D.DLL	MFCO42D.MAP	MFCO42D.PDB
   MFCO42UD.DLL	MFCO42UD.MAP	MFCO42UD.PDB
   MSVCRTD.DLL	MSVCRTD.MAP

HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Build System
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\DataView
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Debug
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Dialog Editor
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Format
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Graphics Editor
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Keyboard
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Layout
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Source Control
HKEY_CURRENT_USER\Software\Microsoft\DevStudio\Text Editor
HKEY_CURRENT_USER\Software\Microsoft\VisualStudio

MSDN Libraries (at least CHM versions) could not be simply moved between OS'es. They must be installed in each OS. But if it is installed to the same folder under different OS'es, the following problem appears: .COL-files, created under one OS don't work under another. For now I solve it in such way:

1. Copy everything from MSDN distribution CDs to single folder. Let it be C:\Program Files\MSDN\CD. CD disks contain some file duplicates. Thus you can ignore warnings about overwriting existing files.
2. Boot the OS, where you want to install MSDN and run setup.exe for MSDN from C:\Program Files\MSDN\CD folder.
3. Chose the only component to be installed - Full Text Search Database (it comes very first in list). Rest files will be taken from C:\Program Files\MSDN\CD.
4. Chose installation folder. Let it be for example C:\Program Files\MSDN.
5. After installation make copies of MSDN120.CHS and MSDN120.COL files. For example for NT4+sp4 it will be MSDN120.CHS.NT4SP4 and MSDN120.COL.NT4SP4. Add to AllUser's startup .BAT-file, which will restore MSDN120.CHS and MSDN120.COL from the copies. Sometimes MSDN120.CHQ and MSDN120.CHW should also be copied. I don't know why, but on my home machine 2 files works perfectly, same time with a little newer MSDN on my office machine all 4 files are necessary. These files are fat, so it is better to make Hard Links instead of dumb copying. Use xln utility for this purpose.
6. Repeat steps 2 - 5 for each OS. Installing MSDN over existing files is very fast. Thus installing MSDN under rest OS'es will not take much time.

These perfect packages require almost nothing. It is enough to copy .LNK files from one Windows installation to another. This step is not mandatory and is provided exceptionally for convenience. When you run any MS Office application, almost everything necessary for its functioning will be written to Registry automatically. But you can meet some small troubles:

• MS Office applications pop up a message, that Tahoma or Verdana font cannot be found. The only thing you need is installing them from Fonts folder of another Windows installation. Note, that this folder usually has System attribute set. Thus you will need to set proper option in order to see it (when installing font using Control Panel -> Fonts).
• Equation Editor doesn't work. In this case you should find "Program Files\Common Files\Microsoft Shared\Equation" folder on your system drive and run EQNEDT32.EXE from it. Equation Editor will configure Registry automatically. For people, who like more tricky ways it is possible to import EQNEDT32.REG from the same folder. This will have the same result.
• Basic doesn't work. I don't know how to fix it. May be Visual Basic should be installed.

To move Photoshop 7.0 it is enough to copy the following Registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Adobe\Photoshop
HKEY_LOCAL_MACHINE\SOFTWARE\Adobe\Adobe Gamma
HKEY_LOCAL_MACHINE\SOFTWARE\Adobe\CommonFiles
HKEY_LOCAL_MACHINE\SOFTWARE\Adobe\Adobe SVG Viewer

And now let's talk about NT4. Photoshop 7.0 setup doesn't want to work under NT4. Obviously this is due to new MSI installer. Thus, install it under w2k or higher, then move to NT4 using described method.

Comments from Axxie: it is little buggy. There are some troubles with user interface - some moment it stops responding on mouse events in some controls. Looks like memory leak. BTW, it seems Photoshop 7.0 could be installed under NT4 with SP6a (not sure).

To move Mozilla 1.7b it is enough to copy the following Registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla
HKEY_LOCAL_MACHINE\SOFTWARE\mozilla.org

About NT4. Same trouble, installer relies on some new features. Install Mozilla under w2k or higher, then copy Registry keys.

To move Putty copy the following Registry key:

HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\Sessions

To move Borland C++Builder 6 you should copy the following Registry keys:

HKEY_CLASSES_ROOT\CLSID\{092E9CBF-071B-11D3-83A5-00C04F6BC736}
HKEY_CLASSES_ROOT\CLSID\{092E9CC1-071B-11D3-83A5-00C04F6BC736}
HKEY_LOCAL_MACHINE\SOFTWARE\Borland
HKEY_CURRENT_USER\SOFTWARE\Borland
and from 
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SharedDLLs
    "<SysDrive>:\\Program Files\\Common Files\\Borland Shared\\Debugger\\bordbk61.dll"=dword:00000001

copy libraries:

%SystemRoot%\System32\*.bpl
%SystemRoot%\System32\qtintf.dll

and final step - add path to Bin directory from Borland C++Builder 6 installation to PATH environment variable.

To move Far copy the following Registry keys:

HKEY_CURRENT_USER\Software\Far
HKEY_LOCAL_MACHINE\Software\Far

To move TheBat! copy the following Registry key:

HKEY_CURRENT_USER\Software\RIT\The Bat!