This is for iPod touch 2g and iPhone 3g only!! Won't work on MC models. This is untethered. Video on how to jailbreak iOS4: http://www.youtube.com/watch?v=dLWLg-1T6dI Where you can find the IPSW you downloaded from iTunes video: http://www.youtube.com/watch?v=3vjUGmnrmvw You will need iTunes 9.2 for this. Heres redsn0w: Windows: http://sites.google.com/a/iphone-dev.com/files/home/redsn0w_win_0.9.5b5-5.zip?attredirects=0 Mac: http://sites.google.com/a/iphone-dev.com/files/home/redsn0w_mac_0.9.5b5-5.zip?attredirects=0 Here's how to jailbreak with todays release. 1. Install 4.0 final through iTunes. 2. Run redsn0w and when you click browse to find the firmware choose the final build. 3. It should be jailbroken know. I have tested this myself and it works.