2 cents: last week i removed one of the processors from my carpc. i was using a spare computer (dual PIII 1G) with 2HD that wouldn't start w/o the car running and couldn't survive reboots (400W inverter).
With everything installed, it was about a bit more than 130W 11Amp draw. after doing a bunch of research, i realized that i was trying to polish a turd. unless i was willing to spend a little money and buy the parts that actualy worked for my system, it was going to suck.
rather than buying larger power supplys to power atx boards with multiple HD's, then determining i need to sell it all on ebay and buy the right stuff, i cut my losses, ate the cost of my 400W inverter, and picked up parts with the appropriate power consumption.
it cost a little money up front, but i've gone from 130w/11a+ to 48W/4a.
moral of the story, i wanted to have a carpc for the cost of the inverter and the display. i found that you get what you pay for, and that route is ok to start, but it's realy going to suck and you're going to spend more time frustrated by the carpc than enjoying it.
in the end, it's cost me $400 more than i anticipated. after a month, i know i'm goign to be appreciating that 400bux for the frustration that it's saving me.
3g Eclipse - VIA M10000/512M Ram
7"WideScreen - XM SkyFi1 - ipod - LinksysWiFi
NetStumbler / Delorme GPS+Maps / Itunes
05 Magnum - AVIC-N2 - xbox