I came across this open source tool a while ago and was very impressed. The nice things about it are that it's open source, it's easy to get started using it, and, oh yes, it works!
The tool name is Dogtail - it's available: here
The technology it uses is interesting too. It uses Accessibility (A11Y) technologies to communicate with desktop applications. This is a key aspect of Dogtail's design. Unlike some other GUI test automation frameworks, Dogtail doesn't "scrape" information from the visual representation of the the application under the test's GUI into a data-store. Instead, it makes use of the accessibility-related metadata to create an in-memory model of the application's GUI elements.
I did not write Dogtail itself - I'm just a happy user. My contribution was some user documentation in the form of articles in Red Hat magazine. One of the article includes a Flash demo.
The articles are linked from the Dogtail entry in wikipedia