While not exactly the Xbox Live Arcade version of Darwinia+, Introversion have released a trailer for Multiwinia, the multiplayer version of Darwinia being released onto PCs, and supposedly one half of the XBLA title.

Simple enough - use your little stick figure Darwinians to kill the other coloured Darwinians. Shoot at them, grabbing powerups, and take over territory. The game is looking quite interesting, having never played the PC original. Something about little stickmen running around and killing each other intrigues me