Perhaps you've already seen this all-in-one case. Its a case with a frontpanel, which works like a usb keyboard. The mainboard is a via epia tc10000 modell. The rams are specially positioned on the back of the motherboard, arranged horizontally and SO DIMM's (laptop ram).

also there is power adapter built in. pics and text (german) here:

http://www.mediacar.ch/carpc-aufgedeckt-5.html

what do you mean?

can i change the motherboard with anotherone which exactly fits?