I have a recent post on the Vista skin for XP, but I recently stumbled across an application called TopDesk that performs the the Vista flip 3D effect. In addition, (which I personally like better), it does the Expose expanded view that Mac OS X uses to switch between tasks. The transition effects are quite smooth.
The only downside is that the program is not for free :(, but I would consider this definitely worth the $15.
UPDATE 23 APR 2007: Read my latest review here.