If you post this in the newbie forum I won't throw you a thinggy but since you post here, I have to
To answer your question, only power and space prevent you from putting a full size desktop as your "carpoooooter". Yes, you can use mATX mobo.
The power calculator itself doesn't do any good with the total wattage.
Take a look at each particular power rail and compare to the PSU you are going to use. 12V rail and 5V rail are the main one you need to look at. When compare to the PSU, look at the "normal" not peak power.
There are probably more people using ATX/mATX than the mini-ITX(VIA) board (I think).
 Best place to start reading is the "Show off your Project" forum. Next is the FAQ and Power forum [/edit]