I have often contemplated something similar to this myself as an added security measure. The big problem is incorporating all of the desired functions into a single unit for a reasonable cost to the average consumer.

1. The recording system should be capable of being in 'standby' when not used. Extended periods of time without driving the car while still providing protection would then be possible. (so a computer that could wake from hibernation or similar to immediately record from an input trigger)
2. A simple micro field sensor designed for car alarms can be used to generate a trigger when any motion is detected. That means if anyone/anything gets close to the car the sensor will activate. The sensitivity can be adjusted with a small pot on most units.
3. Long recording times to capture the most information when most critical.
4. Low power consumption under normal operating conditions. Always think about the worst case scenario in devising your system. ie. you leave on vacation and the car sits at airport parking for a week. Several events trigger the recording over that week, so battery power has to be utilized.

The proprietary system at that link has been designed with all these things in mind...except cost.

An much cheaper solution would be to use the same micro field sensor output to trigger a dc vcr/dvr. With a timed relay you could rig the power to come on, then activate the record button. If only one camera is used it is simple, but if multiple cameras are used one more step is needed. Add a video multiplexer. Audiovox used to manufacture a dc model, but I think it has been discontinued.

I searched for awhile for a vcr/dvr with the trigger input built-in but only found units designed to be used for home security systems. The size was bulky and so was the power consumption.

The bottom line is this.
If you want peace of mind get more insurance. Let the punks steal what they will no matter what security you have.
If you are serious and competent with electronics, more power to you.

I decided even the lower cost of the homebrew system and the time to put it together far outweighed the functionality for me.

More power to you man!

A simple system would be a DVR like this one and a IR camera like this.

The DVR runs on 5v dc or batteries, camera and dvr are very small, it records on SD cards, has multi-zone motion detection trigger to preserve power, and has date/time overlay.

Here's a thread in the GPS section where someone used a similar setup and added GPS overlay to provide car security.

Is the camera going to be in the car? If so you might want to check your local laws. I have read that it's illegal to do that without putting notification on your car that there is a recording devise..... Gotta love the rights we give criminals here.