How to tell which version of Windows is installed?

If you have a non-booting PC with no boot.ini file, and you know it's a flavor of WinXP, is there a way to tell which version of XP is installed? I can boot to a PECD and have access to all hard drive files, but I can't seem to tell which version is installed. I would use a keyfinder type program, but these are not always accurate in reporting the Windows version. They provide the key just fine, but not always the version of Windows. I've had 'em tell me a key was for Pro but it was actually a Home install......

 

Kind of a cheesy way to do it, but you could grab a memory dump file if there is one and debug it on another machine. That for certain will tell you the flavor and SP level.