Boot Your Tethered Jailbroken iPhone/iPod Touch iOS 4.2.1 [Windows] & [MAC] | Apple Devices Informations or UPDATE: Redsn0w 0.9.6 RC8, How to Perform One-Click Tethered 4.2.1 Boot with Redsn0w 0.9.6RC7 [Guide] give you the details on how to script the redsn0w tethered boot.