Well look at this little peanut. It’s the ARTiGO kit from VIA. It’ll set you back $300 and includes a VIA C7 1GHz processor, 4 USB 2.0 ports, integrated audio and video with VGA output, support for up to 1GB of DDR2 memory and 2.5-inch hard drive, and weighs 1.14 pounds.
You’ll have to bring your own operating system (not compatible with Vista), RAM, hard drive, keyboard, mouse, and monitor. The whole setup is fanless and tiny, so it might make a good second or third computer and I bet we’ll see this integrated into cars very soon. At 5.9"(W) x 4.3"(L) x 1.8"(H), it’d fit quite nicely into your standard DIN slot (with a little room to spare) if I’m not mistaken.