Why does my Microsoft Word have a white box with it?

http://i.imgur.com/Mu0Em.png For reference, it's this floating white box. It just started doing this. It doesn't impair function, but it is as annoying as hell after a while.

I'm running Office '08, and my OS is 10.6.8. All of my software is up to date.

Any help you can give is great!