Here’s a slick little gizmo.
The VIA ArtiGo mini pc.
It’s a full PC, with space for a 2.5″ HD, onboard graphics and audio, and up to 1 GB ram. And it fits in a 5.25″ harddrive bay.
I know, I know, there are case modders out there making still smaller PC’s, but this one’s 300$ at Fry’s, no added bother, headaches, or a Dremel necessary.
The specs are decent, but I wouldn’t want to code on it. However, you could probably make a decent Mame cab out of just about anything you have lying around and I’m guessing this would be plenty powerful enough to drive it, not to mention it’d fit just about anywhere without even a second glance.