If the files aren't application files, or settings, why couldn't you simply reinstall XP? It's very doubtful there's something wrong with the disk, it's simply that XP is unbootable. If you're afraid that certain files will be wrecked in the install process there is another thing you could do first.

If you have access to another XP machine you could transplant your C drive, copy the files off of it and then proceed to reinstall your copy of XP (edit: sorry I missed that you'd tried this, but you didn't say if it was an XP machine or not, I seem to recall that the flavor of NTFS used on XP differs from that used on W2k). Chances are the files you copied will be waiting for you after the install, but if you're paranoid you could do this. Of course you will have to reinstall all you applications after the OS reinstall, which is a PITA but takes nothing more than time.

Whatever you do, do not format your C drive until those files are off of it! I've not got XP, but other versions of windows don't require a format before install.

Oh yeah, one other thing: Don't Panic.

(with thanks to Douglas Adams)

Good Luck!

-Zeke