If you don?t have a display driver capable of running WDDM you?ll get the Windows Vista Basic theme which does not benefit from some of the more graphically intensive features such as desktop composition and glass window frames. This is a good, clean interface called the Basic or Standard theme, but lacking the glass window frames of Aero?. Community members have rightfully complained about this theme, and we agreed (actually we always knew we?d fix it in a future build). When will it be replaced? Sorry -- we can't share that yet, so stay tuned. What does it look like? Well, here's a screen shot. Enjoy!

Windows Vista Team Blog