There are a number of programs available to turn your iPad into an external monitor in Windows. The most recent of these was released by Displaylink (http://www.displaylink.com/support/downloads_ipad.php). The big difference with this application is that it supports the Windows 7 Aero interface. And it’s FREE.
Initial testing so far indicates that it is also the fastest driver around so far. One issue I have run into is that it occasioanlly runs into a connect-disconnect loop, rendering the screens unsuable, until the app on the iPad is stopped and restarted.