If you have a linux boot disk and can get into linux on the HD, you could, as root, edit /etc/lilo.conf and then /sbin/lilo to fix lilo. Or, you may be able to edit it from Knoppix running from CD. Or:

Fix MBR
If your master boot record is broken, and you want to repair it with Knoppix, read the readme file in /knoppix/user/share/docs/mbr. It tells how to make an mbr boot floppy that I have used to boot win98se. You do it as root from a terminal. The command, after su to become root, is like these command examples:

install-mbr /dev/fd0 -T /dev/hda

Install the default MBR image on /dev/fd0, taking the partition table from /dev/hda.

install-mbr -kr /dev/hda

Reset the parameters on /dev/hda without installing any new code.