The missing file is a significant part of your Registry and running Checkdisk has been known to fix the error that's keeping it from working properly.
A borrowed XP CD should work - you start of seeming to be reinstalling but then need to go for the Repair option, select the version you want to repair - normally No. 1 - and at the Command Prompt, type chkdsk /r (including the space before the /) then hit Enter/ It's a lengthy five stage process which may get to 70% and seem to revert to 50% but let it run its course - it might do the trick.