Since apparently Apple now provides Windows iTunes 10.5 for iOS5 and iCloud developers, its no longer the case that only Mac owners can legitimately activate their devices. We now provide a Windows version of redsn0w for those developers (only!).
You can learn more about the RedSn0w .9.8b1 release and find the Mac tutorials here. The Windows tutorials are coming shortly.
Remember this is a tethered jailbreak and intended only for developers. Unlockers especially should stay away from this because restoring to iOS 5.0 will upgrade your baseband (unless you use Sn0wBreeze) and UltraSn0w has not been updated for 5.0 yet.
You can download the new Windows version of RedSn0w here.
● iPhone 4