Finally a tool for Windows to jailbreak the iphone, it is called blackra1n . It will Jailbreak version 3.1.2 on the iphone 3G, 3GS and ipod touch according to http://iphonejtag.blogspot.com/. If you want to download it, the link is below. When the page opens just click on the Windows logo towards the bottom.
HOW TO USE THE Blackra1n Video: