If it's Linux mandrake, just put the CD into the drive and boot off it... When it asks you whether you want to install/upgrade choose upgrade, and let it run through the stuff. You'll have to reconfigure networking etc, but after that you should have your Lilo back...
If it's any other Linux distro, I guess you can do the same, or just create a boot disk and install Lilo again from console.
regards
packetMax