Yes, sadly, Knoppix and Linux in general have a tough time with M$ proprietary NTFS file system.

Have you tried taking your XP install CD and booting into the command console? If you know what the offending files are, you should be able to delete them using that.

If not, then you should get a CD that will boot you into a limited Windows environment:
It's Bart's PE:

http://www.nu2.nu/pebuilder/

Good luck,

SakiZ