if FC5 uses grub?? then you should just be able to copy the menu item from /boot/grub/menu.lst on hda3 and put it in the menu.lst on hda1 just change "root (hd0,0)" to "root (hd0,2)"
If FC5 doesn't use grub then it's still easy to setup
you edit /boot/grub/menu.lst on hda1 and add something like
title Fedora Core 5 (on hda3)
kernel /boot/vmlinuz-2.6.xx.. root=/dev/hda3 [kernal options]
initrd /boot/initrd.img-2.6... (if using an initrd image)
savedefault (to have grub have the OS selected on next reboot)