An enterprising group of hackers have ripped apart Google's Android operating system and posted an x86 version that'll run on your desktop computer, so you can try out the open-source OS without buying a G1 or HTC Magic.
It's only just hit version 0.2, so relatively few video and network card drivers are working at the moment, but the team asks you to contact them if yours doesn't function, so they can add support. At the moment, it's very similar to the phone version, Cupcake 1.5, but the makers say they want it to be a "real OS" in the future.
If you fancy giving it a try, all you need to do is download an ISO file, burn it to a CD and then boot your PC from that CD. It'll work in a virtualisation application too, like VirtualBox or Microsoft Virtual PC, if you want to try it without a reboot.