You could buy an external dvd drive enclosure with a firewire output and fit a cd driveinto it (or a dvd burner if you want). I've done that. But any external unit should work as long as it's got a firewire connection. My Macs are Intel but that should make no difference at all.
MCE has a great line of both external and internal Mac drive upgrades, all guaranteed bootable. You could actually put a new dual layer DVD burner in there for only $99.