Get the windows install file of the bootdisk here:
Create the bootdisk and then boot from it. Make sure it's a better quality floppy, it failed on all the cheapo floppies I tried.
Once it's booted login as root and mount your / and /boot partitions. Depending on the drive and partition numbers do something like:
mount /dev/hda6 /mnt
mount /dev/hda1 /mnt/boot
Then edit your the file /mnt/etc/lilo.conf
And finally reinstall lilo with the following command.
chroot /mnt /sbin/lilo