You need to boot into Linux and re-run LILO. Look at your /etc/lilo.conf and see what partitions you have listed and make sure it is writing LILO to /dev/hda1. If all looks well in /etc/lilo.conf then do this:

su
<password>
/sbin/lilo

It will output text to the screen. If it doesn't error then try a reboot and see if you get a screen from which to choose an OS. If it errors after /sbin/lilo or it still won't boot Linux post your /etc/lilo.conf file and we'll try to get it fixed for you.