I am planning on putting together a UAE machine and decided to buy a mother board that I could stick inside of a NES.
I want to use an externa Pico PSU, but am unsure what wattage I'd need with this, or what sort of PSU goes with the Pico device once you've got one.
There are boards out there with DC power input built in which saves you the cost of the Pico PSU. They have a SATA power connector on the board for powering your drives. I think it's probably limited to powering 2 devices max but shouldn't be a problem, especially if you're not considering ad optical media.
If an Atlhon 5350 (quad core @2Ghz + Radeon 8400 TDP 25w) would meet your CPU and video requirements I'd recommend an ASRock AM1H board as a cheap and cheerful option.
http://www.asrock.com/mb/AMD/AM1H-ITX/If you want plug NES controllers into the front ports like normal then there's an adapter for that here.
http://www.raphnet-tech.com/products/AnodeNES_circuit/index.phpThe connectors aren't fitted as standard so you can just solder some pins in and wire it to the controller ports already fitted to the case.