... not to mention running Retail is a no-go (unless you find the appropriate settings, export them to a .reg file on the USB drive, and apply them for each computer you use).
Some of the keys are: (found by using Start->Run regedit Enter)
My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Volition
and
My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Volition, Inc.
and
My Computer\HKEY_CURRENT_USER\Software\Interplay Productions
(this one I think is just for registration and so MIGHT not be necessary)
and
My Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Management\ARPCache\FreeSpace2
(this one I have no clue what it is; it also MIGHT not be necessary)
and
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\FreeSpace2
(this one is only necessary for Un-installation via Add/Remove Programs)
and
HKEY_USERS\.DEFAULT\Software\Microsoft\Windows\ShellNoRoam\MUICache
(this one I again have no clue about its purpose, so...)
and
HKEY_USERS\S-1-5-21-2000478354-562591055-682003330-1003\Software\Interplay Productions
(this one...no clue...)
I think Retail might run fine with just the first two, maybe even just the first one, seeing the second one contains almost no data. (I think its the version number or something like that, if so, it's not even accurate.)