Just do what I did. Go to http://www.newegg.com and buy a Pioneer DVR-A05 DVD burner (same drive they use in the PowerMacs), and buy a 5.25" Firewire enclosure for it. It couldn't be easier to install the drive in the enclosure yourself (it only takes a screwdriver), and you'll save a couple hundred bucks.
By the way, this is also the best way to make a Firewire hard drive as well. Those enclosures have a power supply and a small interface in there that converts from Firewire to IDE, so you can connect any IDE device up to your Firewire bus.