A 36-year-old chap called Russ in Arkansas USA, who also goes by the YouTube handle of "russm313", has built a tabletop Nintendo arcade cabinet.
He says it took about a week, cost about $70, and during the process he drank 2 cases of diet coke. It's made of MDF and has USB ports, a single power cable, and the option to plug in two original NES controllers.
Inside is a PC running Windows XP and a NES emulator, hooked up to a 17-inch monitor. The joypad can be switched between control mode for running games and a mouse mode for controlling XP. Alternatively, you can plug in a real mouse and keyboard.
There's full detail on how Russ put it together on his blog, a link to which is below. If you're not interested in the nitty gritty, and you just want to see the thing in action, then hit "play" on the video above.