Microsoft's Monaco - The Windows Garageband

Here's news about a new program coming with Vista

GarageBand is Apple's MacOS application for amateur musicians. It comes with 1,000 pre-recorded sampled loops, and 50 sampled or synthesised instruments that can be played using a MIDI keyboard connected to the computer, or using an on-screen keyboard.
Monaco will be aimed at the same audience, sources said, and will be positioned in the same way – except that it will work on Windows only. Microsoft also is expected to play up Monaco's use of Microsoft-devised search algorithms for finding particular music clips.

http://www.microsoft-watch.com/article2/0,2180,1947454,00.asp