I got the supply used from someone at the MP3Car forum. It's full ATX, 2.01. I like the PCPower model mostly because of the 1U form factor, which would allow for a much smaller enclosure. I think it may only be 100W though. If you are comfortable making your own, there are parts and plans to be found at the MP3Car forums for a couple of very small DC-DC supply. Fairly simple design, but not something I wanted to deal with.

I think the hot ticket for this stuff is going to be the new mini-ITX boards from VIA. They have an onboard power system and take 12VDC directly. I'm just waiting for a faster processor to become available, because it uses an embedded C3, which isn't all that great.

OS is WinXP. MS is working on a more graphical home-theater oriented OS too, should be out in a few months. I think it's called Freestyle or something. That might turn out to be very good for cars too.