I just wanted to share the cool mouse I bought, since I haven't seen any threads on it. It's a Flex Pointer - made mainly for presenters, but perfect for a car PC.
It is USB and runs on RF. You just plug the receiver into the USB port and it works for 10meters, through walls, in any direction. I tried walking all the way to the other end of my house when I first got it and it still controlled the PC.
It's got a little disk in the middle that works as a full mouse with right and left click buttons. On the side there is a jog dial that is used for scrolling and dragging when pushed in. It also has a built in laser pointer, which is absolutely unecessary for our use, but pretty neat. Just need to make sure to stay out of trouble with it It requires two buttons for a few seconds to turn the laser on and off so you want accidentally blind other drivers.
The only disadvantages are that it can be hard to adapt to - its tough to click and move the pointer at the same time and if you are pointing it at an angle (i.e toward the screen) you have to rememebr that up from the mouses perspective moves it up - not quite like a regular mouse. It lags on some computers. I tested it on three and it runs great on 2 but lags on one. There is more than likely a cause and solution for that, but i didn't care enough to investigate.
$50 is a little pricey, but I think it's worth it. I got mine for around $40 shipped on Ebay.