TooManyCars.com has updated their family tree style poster of how all of the car companies are related. The latest updates were as of 4/1/08. They have also changed to better software used to zoom into the poster. Each of rectangles you see on the images will zoom in close so you can read the details about the connections.
They've really done a good job tracking down the specific types of relationships and the ownership portions between the companies. High-res PNG or PDF files are also available.