I have the sane problem, and a bit of research suggests that any change of the Windows partition will cause Windows to misbehave -- including refusing to boot, even if the files you can normally see are not changed.
This suggests you will have to wipe the Windows partition and reinstall everything from scratch, which means you will eed your original CDs and CD Keys.
I wish some expert could show why this opinion is wrong. It if is wrong you might try iPartition. The vendor of VolumeWorks says you should not even try -- your Windows partition will become unbootable.
If you are ready for a re-install of XP, first try and clone your current XP environment to an external firewire drive.