The official Shadowrun forums declare that a demo will be released, er, half an hour ago on Xbox Live Marketplace. So, 2am PDT.
There's no sign of it yet according to Internet hero Kristan Reed, and apparently there's no immediate plan for a Windows Vista version ("We haven't announced [it]").
Update: It appears to be sitting pretty now on Live Marketplace, weighing in at approximately 1.07 GB.
The Xbox 360 demo includes the first three training chapters, bot and online multiplay, the Power Station level, Elf and Human races, four types of magic, three types of tech, and six weapons including the katana.
Specific details are all on the forum.
Shadowrun - released last Friday - is an online multiplayer game derived from the pen-and-paper RPG series of the same name. One of its headline features is the facility for PC and Xbox 360 owners to play against one another on the same servers.
For more on how it all works out, bob your fairy way over to our Shadowrun review, which takes in both versions.