Two modules I just learned about today are Win32::Setupsup, which has the handy method SendKeys() (send arbitrary keystrokes to any window on the desktop) and Win32Guitest. (Dunno if that one's on CPAN or not.)

You'll certainly want to visit Jenda Krynicky's archive for all of the GUI goodness.

(okay, I read about them in a book. I don't even HAVE Windows.)