Not being afraid to work in the car environment, get one's hands dirty...all plusses!
I read the mp3car forums and printed out a lot to study and make notes on for three months before beginning to make purchases.
Some of my experiences:
>Used an inverter to supply 120vac to deshtop unit mounted in cargo cmpt of station wagon. Inverters are generally frowned upon, but I have no beef so far, except for the tiniest buzz in audio... remember that mst use a dc/dc converter to power carpc's. See mp3car store for some neat stuff to salivate over.
>Didn't want to change any stock dash installs (as yet), so mounted 7" vga monitor on flex gooseneck mount on seatbolt.
>using wireless kbd from mp3car store ($70)
>have usb cable running to dash, plugged into 4-port hub. very handy.
It's lots of fun, and there's no one way to do it. helpful hint: do not consider mounting anything in the not-so-clean under-seat environment. As DarquePervert said "you don't want to fart on your computer" !!