I am not sure what distro you installed? I am assuming Redhat/Fedora
Boot your system with the first Install CD. At the
prompt, type linux rescue
Follow the instructions.
When you are dropped at the # prompt, type
chroot /mnt/sysimage (all this info is given to you during rescue... read the screens carefully).
grub-install /dev/hda (again I am assuming it is your first disk)
exit and reboot.