After downloading the title, the normally $29.95 PC game can be played for free from Friday through Sunday. Like many Steam-purchased titles, the game can be downloaded and preloaded by German gamers before Friday and played once the free weekend begins.
Although this free weekend doesn't include North American gamers, Valve representatives have previously stated that a free Team Fortress 2 weekend would be coming in the States as well.
I hope Nintendo tries something like this with some of their Virtual Console games... that'd be pretty cool.
Unfortunately, Nintendo has shown pretty much no savvy in advancing their business using the Internet. They're kind of accidentally stumbling in the right direction at times with some of the functionality of the Wii, but it's still pretty sad overall. I don't think they yet possess the required cunning to figure out that promotions like this would work well.
Maybe I'm just bitter because I like my Wii, really like my DS, and love the Internet... but any combination of those 3 still sucks balls thus far. :(