How to Jailbreak iOS 4.2 GM with redsn0w 0.9.6b2
The new version of Redsn0w is also updated with two new features, which enable you to make a custom boot logo for iPhone 3G/iPhone 3GS/iPod touch 2G and to implement the "DFU" button in Pwnage Tool, which makes your device ready for a custom DFU. The latter option is available for both Apple and Windows users. All you have to do if you own a Windows-powered handset is to run the new version of redsn0w.
For more information check out the links below and don't forget to tell us how it worked after you did your jailbreaking exercise on iOS 4.2 GM.
source: Dev-Team Blog via Redmond Pie