If you don't want to track down a 2.5" drive and cable, you can remount a 3.5" in a 1200 desktop very easily with a 2.5"->3.5" kit or cable - it just needs to be a rather thin drive. It'll fit very nicely on top of the metal shielding and beneath the keyboard ribbon. Just make sure you've got something insulating the drive from the metal! I use a small piece of foam in mine.
