As you know that Sn0wbreeze cooks custom iOS firmware and lets you to jailbreak idevice without upgrading the baseband on Windows Operating System.
iH8snow, the developer behind snowbreeze, has just tweeted that you can use Snowbreeze for iOS 4.2 only if you have already saved the SHSH Blobs for iOS 4.1 and beyond if you are on previous iOS version.
iOS 4.2 GM Build is already out and according to some hints the final and public iOS 4.2 release is coming on November 9th or 12th. Once iOS 4.2 is out, Apple will stop signing the iOS 4.1 at any time.
So it is highly recommended that you save the SHSH Blobs for iOS 4.1 now. Follow the complete instructions posted here to save the Blobs on Cydia Server or on local storage device with TinyUmbrella.
Moreover, the next gen jailbreak for iOS 4.2 will be untethered for only those who will have saved the SHSH Blobs for iOS 4.1, otherwise they will get tethered jailbreak.