I don't know if this is possible with SATA drives (I have one, but I still boot from IDE), but let's hope there's an analog:
With IDE controllers (and IDE drives) you can change which drive is looked at first, in the boot priority, by moving all of the jumpers to CS (Cable Select) and then making sure the drive you want to boot from is plugged in to the IDE0 channel (as opposed to the IDE1 channel). As it were, there are - basically - four IDE channels: IDE0, IDE0-1, IDE1 and IDE1-1. As long as a drive with a bootable image exists on the IDE0 or IDE0-1 channels, you'll boot from it.
So, what my thinking is, if SATA has "channels" too, put the 500GB, Fedora Core 8 drive on the first SATA channel, and then edit the Grub menu to your heart's content.