go to this site:
download the "grub.img" and "rawrite.exe"
make a grub floppy disk.
reboot the PC with grub floppy in the drive (in BIOS boot sequence, the floppy should be first)
once in grub, type
where x is the disk where is your linux /boot (x=0 is hda, x=1 is hdb ...) and y is the partition (counting from 0, then hd0,0 is the /dev/hda1)
then you can access your kernels. try to type:
kernel /vmlinuz ro root=/dev/hdjk
where jk is your / partition (like hda2 or whatever). NOTE if the /boot partition is the same as / partition you should use
kernel /boot/vmlinuz ro root=/dev/hdjk
then try to type
(or initrd /boot/initrd.img if you have /boot and / on the same partition)
if you do not get errors like "file not found", type
and your linux should boot (with some errors, but able to reinstall /sbin/lilo)
If you have problems, you must study the grub commands in more detail (or tell us the partitions of you disk and the parameters used by lilo to boot your kernel). To check the exact configuration used by lilo, you can cat the /etc/lilo.conf in the grub shell. Just use:
where z is the disk and g is the partition (both in the grub syte) of you / partition
beware when you reinstall lilo: you might lose windows XP! check lilo.conf carefully.