Where can I pick up a computer to diagnose problems on my car.

A few months back I was reading in a magazine article on one that you could purchase and install in your car and after a week it would give a full report and any errors in the vehicle that you could look at on the pc.

Any help?

I think this is the thing you probably saw.
http://www.davisnet.com/drive/products/carchip_products.asp
You'll need an OBD-II connection...'96 and up. I'm stuck with a '95. :s