Finally, you can stop watching rushed, pointless Okamiden trailers Capcom puts out every five minutes and actually play the damn game.
A playable demo has been released, but you'll need to download it via the Wii's Nintendo Channel. Of course you'll need a Wii that's connected to the internet to get it.
To download the demo, put your DS in 'Download Play' mode, and on your Wii click through to the Nintendo Channel's DS Download Service.
The demo is apparently only likely to remain available for a week, so no faffing if you fancy a go.