"C is for cookie anyone" anyway, I have X.1 running on a rev a iMac with 512 meg of RAM and on my 233 laptop with 160. More Ram helps, max it out if you can. I'd recomend a rev a with 512 over a 500MHz iMac with 128, RAM is that important.
oh, and don't expect to do crap with openGL if you are on an iMac. productivity? fine. Quake? or even nanosaur? crap.