I've just finished installing and working the bugs out of my CarPc, I started with a 350Mhz comp with 393 MB RAM, and quickly realized that wasn't enough. so here's what i'm running now
PC
AMD 3500+ 2.2Ghz
MSI K9VGM-V Motherboard
Geil 512MB PC4200 DDR2-RAM
7" Lilliput Touchscreen
30GB HD
Audio
300 watt RMS 2 Channel MTX AMP - running 4 speakers
500 watt RMS D-Class MTX AMP - running 12" Sub
2 Front - 5 1/4" Sony Xplods
2 Back - 6 1/2" Sony Xplods
12" MTX Sub
I am currently using roadrunner as my front end and loving it, hoping to install GPS (iguidance) by the end of the year.
The start up time is 20sec the off time is even less.
here's a vid of the start up

shutdown

here's my trunk

here's some other screen's









and some other video's


Total Computer Cost
7" Lilliput(Plus Customs) = 377.11
3500+ 2.2 Ghz CPU = 113
VGA/USB/Power Cords = 154.61
800 watt Power Inverter = 112.99
PSU =21.09
512MB RAM = 69
Motherboard = 71
Total Cost = 918.90