boot your cd with: #Note: command line commands are bold and edits are italic
knoppix 2 #which will get you running as root in text mode
then mount /dev/hda3 /mnt/hda3
and then mount /dev/hda7 /mnt/hda7
then just in case the partitions are mounted read-only
mount -o remount,rw /dev/hda3
and mount -o remount,rw /dev/hda7
then cd /mnt/hda7
then chroot /mnt/hda7
now using an editor (ie,: nano or another editor) look at and if necessary edit your /etc/lilo.conf file and make sure your:
boot entry is: boot=/dev/hda3
and root is: root=/dev/hda7
then (assuming the rest of lilo.conf is OK) re-run lilo:
/sbin/lilo -v
and note any errors, if you don't have any errors then use dd to copy the bootrecord to floppy (necessary if you are using ntfs on your xp install):
dd if=/dev/hda3 of=/dev/fd0/linux.bin count=1 bs=512
then follow (garyng's) directions to put linux.bin where it's needed on your xp system and edit your boot.ini (or whaterver it's called ... to chain boot the knoppix bootrecord)

Sorry I can't help you any more regarding xp, I've really never used it.

HTH

~rock