ok from my experience with dsl and puppy
a 866 mhz p3 coppermine with 512 ram can run these os with no problem
i did get a small system for fun once
it was a p3 866 mhz with a via chip installed on the motherboard
all was on the motherboard the video lan sound
i used a small 7 inch or so lcd for the monitor
no harddisk only usb (128 mb)
was cool i dont think u can get your 12v power to run the motherboard!! i used a 350 w power supply to power my system
i think that all red wires connected to the board are 12V the others are of different voltage like the yellows are 5V you should get something while goggling on the net
try
http://www.subzeropcs.com/thermaltak...pu_cooler.html
it should make your machine completely silent
hope these help