George Hotz put out an iPhone 3GS jailbreak for Windows, with OSX to follow soon. This allows the installation of third-party software not approved for Apple's appstore, but doesn't unlock it for use with T-Mobile or other GSM networks.
Download it. Make sure you have windows(but not 7), the latest iTunes installed, and an iPhone 3GS with 3.0 firmware. Connect your iPhone normally. Click "make it ra1n". Wait. On bootup, run Freeze, the purplera1n installer app. Hopefully you'll figure out what to do from there.
Hotz explicitly calls out the iPhone dev-team for waiting until 3.1 to release the crack.
Normally I don't make tools for the general public, and rather wait for the dev team to do it. But guys, whats up with waiting until 3.1? That isn't how the game is played. We release, Apple fixes, we find new holes. It isn't worth waiting because you might have the "last" hole in the iPhone. What last hole...this isn't golf. I'll find a new one next week.
Fantastic. I wonder if this alternative release will provide Apple with an opportunity to quickly jail the 3GS again in 3.1. Preventing just this scenario was ostensibly the reason for Dev-team's decision to wait.
I make it ra1n [iPhonejtag]