Can you help me? :( I've ruined my windows 7, that was installed in a dual-boot with windows xp, making it un-boot'able. So now I'm back to using my good old windows xp, and I want to remove windows 7 without formating the hard drive because there is too much important files in that drive and not enough space in other drives to back them up.
Well, the safest thing is to leave the program files directory as you can't be sure what belongs to Windows XP and what belongs to Windows 7.
I would just delete the Windows folder (which ever one is from Windows 7 - I take it you know which one!).
Then, as you will have the Vista/7 Boot loader, I recommend you download EasyBCD and remove the Windows 7 entry.
There are other ways that you could free up a little more space, but, I think this is the safest and easiest.
Using Windows 7 boot manager to boot just Windows XP is a strange "solution".
You can always mark XP partition as active and run StartUp Repair using XP Recovery.
For more advanced users - you need to write:
1) XP MBR.
2) XP PBR to XP partition (should be active).
3) ensure ntldr, ntdetect.com and boot.ini on active.
4) ensure boot.ini has correct ARC paths for XP.