We're releasing more details about Windows Movie Maker on Vista. Check out the following link for a few more details.

Link

One of the most exciting features (besides the fact that you can now use Windows DVD Maker to publish your MovieMaker projects directly to DVD), is that we now take advantage of the graphics processor on your video card. This means that you're no longer limited to the 320 x 240 preview that we currently have in MovieMaker on Windows XP.