Thanks so much for your input. I have a wireless mouse, but alas, it is not compatible with Windows 7. I'll get a new one tomorrow, disable the touchpad when I play, and see if that works.
The weirdest thing has been happening in my game, and though I've scoured the Internet, I haven't found anyone else with this particular problem:
I start B&W, and usually gameplay is fairly normal. However, after anywhere from a minute to a half hour, my cursor will fly out over the ocean...