Have you looked at this thread?

http://www.knoppix.net/forum/viewtopic.php?t=1075

I expect you are using the xp bootloader, I can't help you there as I've hardly even seen xp run, but I know I've seen posts about setting up the xp bootloader, so you may be able to use the same approach as the lilo setup in
oscar's second post.

HTH

rock