Redsn0w 0.9.7 for Windows Will Untether iOS 4.2.1 Jailbreak with iOS 4.1 Firmware. Expected to Release Soon!!
The iPhone Dev Team has confirmed that a Windows Version of Redsn0w 0.9.7 is on its way for jailbreaking iOS 4.2.1 with iOS 4.1 IPSW instead of iOS 4.2b3 firmware and SHSH blobs.
Since Apple still serves the 4. IPSW (not blobs!) , we'll do a windows redsn0w release for untethered 4.2.1 via Monte -4.1
Unfortunately, it wouldn't be really fast as the Windows version of Redsn0w will be using filesystem instead of RAM.