RedSn0w has been updated to jailbreak iOS 4.1 on the iPhone 3G and iPod touch 2G
This is a beta release of redsn0w for the iPhone3G and iPod Touch 2G at FW 4.1 or 4.0. It uses the same pwnage2 DFU-mode exploit that we've been using since the 2.x days. It does not include the SHAtter exploit developed by pod2g. Nothing new is revealed to Apple with this jailbreak.
IF YOU USE THE ULTRASN0W UNLOCK, PLEASE WAIT FOR PWNAGETOOL TO SUPPORT 4.1. DO NOT USE REDSN0W. That’s because to use redsn0w at 4.1, you need to already have updated to official 4.1 from Apple. If you do that, you lose the ultrasn0w unlock (possible forever).
Currently this RedSn0w 0.9.6 release is Mac OS X only; however, a Windows very will come in the near future.
You can find instructions on how to use RedSn0w here. Simply download this new RedSn0w build and use the 4.1 ipsw instead of the 4.0 one in the tutorial.