Yep, miniMac as a CarPC crossed my mind too. one of the nice drive-bay controls would work for mp3 duty. This one is minimalist but you get the idea:
<img src="http://www.crazypc.com/images/cases/caseaccessories/lcd/mx213full.jpg">
Rawb, they're supposed to ship this month. Complications can arise but most big manufacturers have learned wallstreet doesn't like lots of lead-time from announcement to delivery. Standard procedure is to announce
after inventory buildup has begun. I'm crossing fingers MacWorld fever didn't corrupt.