if you can, snag an old laptop. no dc conversion problems (use a regular dc-dc car adaptor for the laptop)...much smaller...much less heat issues...laptops are better able to handle shock/vibration.

i know you have the desktop already, but if you see a laptop around, grab it or maybe trade the desktop + some cash for it. toss a 802.11 pcmcia in it, and it will make everything easier!