Thanks to a link from Tomas, I can now control my iTunes visualizer!
You can find a list of commands for your iTunes visualizer at this site. It always bothered me that I couldn't control that and now that I can I might use the visualizer more often. I may have heard that this is just an implementation of whitecap or some other common visualizer but I'm not sure. Any documentation from Apple on this would be appreciated.

A favorite: DT Sine:Free Yourself:Quicksilver