A "spy" cam will not work in a car because you need to be able to record the events. Unless you want a VCR in your car, forget it.
The better route is to do this:
Get a wireless 802.11g camera with infared
Hardwire it into your car
Have it connect to your wireless access point
Optional: Get a server and have it record everything (I mean every single second).
This is better because you can pull up the feed anytime from your computer. You can even look at the camera if you're in another country, but your car is still at home. And since you have a server running and recording the footage, you can pull it up at anytime.
Another thing you could do to get creative is wire it up to one of your alarm outputs. That way, when the alarm gets triggered, the camera will come on and start recording.