I have a Clarion AutoPC in mine - does navigation, MP3s, radio, CD changer, voice guide and more. It took me 4 hours to install - and it can be had off Ebay used for about 200$. If you do your own carputer from scratch, it's a good idea to get IDE-to-flash adapter and boot off a large-capacity flash card (e.g., CompactFlash) for almost instant-on boot process. With USB and EarthMate GPS (and MS Streets and Trips) you could have a very decent navigation system (I'm assuming you are going for a 7" LCD installed by the windshield or the temperature controls). You may need to change to a stereo system with AUX-in port - or get a diagram to somehow hook up to the car's sound system for MP3s and such. They also sell nice micro-keyboards on Ebay, that measure about 6" x 4". Let us know how it goes.