Redsn0w 0.9.6 is now available for Windows. You can use it to jailbreak iPhone 3G and iPod touch 2G on iOS 4.1. If your iPhone 3G relies on Ultrasn0w unlock, stay away from Redsn0w as it updates your baseband to the latest version, making it impossible (for now) to unlock.
Redsn0w 0.9.6 can also jailbreak iOS 4.2 on iPhone 3G and iPod touch 2G. Proceed at your own risk only.