MiniPC of Japan has released a small PC (6.2"x5"x2"), where you'll have to sacrifice quite a bit of power to get a box priced anywhere close to a Mac mini. It can be outfitted with a Celeron M420 inside with 256MB of RAM for $887. If you want a setup with an Intel Core Duo, well, that'll cost you $1397, but you get 512MB of RAM.
We're not quite wrapping our minds around this one, since a Mac mini is priced much lower than this, with a Core Duo mini starting at $799, and it lets you boot both Mac OS X and Windows XP. Maybe MiniPC's customers in Japan haven't heard of the Mac mini...?