There's no word yet on what the demo will contain and there's also no word if the PC demo will support things like the 3D support and the advanced Nvidia PhysX in-game physics that are promised for the full PC version. We guess we will have to wait a bit longer to find out.
Update: 2K Games sent over a note saying the Mafia II demo takes place in the 1950's where "Vito and his buddies, Joe and Henry, are sent to take out a mobster known as 'The Fat Man'". What, where's Jake?
Gallery: Mafia II Screenshots