Check out this cool PC Mod, made from a moded Nintendo Game Cube.
The PicoCube uses a Pico-ITX motherboard, there is also 1GB of RAM and a 100GB SATA hard drive.
Power comes from a Pico PSU and there is also 4 USB ports, and the moder even had a DVD drive in there, but he had to remove it due to the heat inside the tiny case.
The PicoCube runs a custom Mario themed version of Ubuntu 8.04.
WiiDS Podcast via Kotaku