Jeff installed CentOS and Fedora yesterday but kinda broke GRUB. Now I managed to fix it with my usually tendency of fixing things right before the end of class and leaving without blogging. But here we go.
CentOS is on sda1, swap on sda2 and Fedora on sda3. I will tell you my solution to the problem but mind you this won't always fix GRUB. I mounted sda1 and chrooted into it so I could access the /boot/grub. I opened menu.lst and copied the entries for CentOS. I then opened the same file on the Fedora partition and copied the entries to the menu.lst there and commented out hiddenmenu.
I believe what happened is GRUB was installed on CentOS and then Fedora as Jeff said. Now GRUB was configured to boot just into Fedora silently since it believed there was no other OS. By copying the entry from menu.lst in CentOS to the one in Fedora it told it GRUB where to find CentOS. Commenting the hiddenmenu option out also meant that when you boot you got to see the GRUB menu again. The End.