I've finally replaced an old Quicksilver G4 tower from around 2001 at my parent's house with a 20" Aluminum iMac. So, the troublemaker that I am, took their old tower. Perfectly good machine, just needs to be upgraded a bit. However, being as old as it is, it does not even have a combo drive in it to play/run DVDs. I want to put tiger on it, and watch dvd's. What should I do to upgrade the optical drive? What model should I try and find? Is eBay my best option? Any suggestions?