http://support.microsoft.com/kb/158238 lists the OS's for Windows ME through Windows 95.
it comes from the key
HKEY_LOCAL_MACH INE\SOFTWARE\Mi crosoft\Windows \CurrentVersion[VersionNumber]
and you don't bother with the appended A's and B's because that is in a different entry.
Microsoft doesn't have such a list for newer OS's, unfortunately.
HKEY_LOCAL_MACH INE\SOFTWARE\Mi crosoft\Windows...