I got a TH-5688 5.6" LCD from MP3cars.com. It's bulkier than I liked but weights very little. It's only $125 and the quality is not very good. But it serves my purpose well. I am road testing it now. My setup is:

PII 300 Laptop
192MB memory
DVD + MPEG2 decoder (for playing DVD)
8GB HDD (lots of MP3)
Mappoint + USB GPS (still trying to get it to work)
145W DC/AC inverter
5.6" LCD
wireless mouse/kb
FM modulator

I had it running for couple of days now. Everything seems to work fine. Gonna work on installing couple of cameras on front and rear bumpers for forward/backward bumper view :-)

also working on a power on relay system so the system will turn on/off by itself whenever I start the car,.
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Would like to hear about your setup.

John