I'm running Windows 7 64-bit and have my video drivers updated.
Resizing the window fixes it until I move my mouse back into the window.
I've also tried redownloading it from the Arduino website, no luck :/
Check one of my other replies regarding Java2D. There are a few typical debugging options you can try, in order:
I forget where to set properties on the Arduino VM on Windows. You can probably hack the Launch4J config.xml in the Arduino installation directory.