Before making the changes to lilo.conf, look for a 512 byte file in /boot (probably boot.0300) and check that the date matches the installation date. lilo -u will put the stored bootsector back where it came from. Failing that, dd if=/boot/boot.0300 of=/dev/hda bs=446 count=1 will restore it by hand.

The extension is based on the device numbers, so if you already moved it to hda5, you should have two boot sectors sitting there.