I ran Quake 1 on a 486/66DX2. I'll wager that a dedicated enough programmer could wrangle it into running on the iPods at a playable (if not enjoyable) frame rate. If you're taking the requirements from the Wikipedia article, those are the "Recommended" specs, rather than the minimum. The official requirements simply list "Pentium Processor" without any given speed. But either way, it'd be nice to see someone try it just so we can finally put up a flag saying "There, it's been proved to be impossible" or "There, this is the upper limit"