Sn0wbreeze is live for windows users.

Scott Herder 2011/02/15 0
Ih8sn0w has released a new version of Sn0wbreeze, Sn0wbreeze 2.2. (aka PwnageTool for Windows.
This is great news for windows users since it will allow you to create custom iOS 4.2.1 firmware files on your PC. It uses the GreenPois0n exploit, which gives those windows users that beloved untethered Jailbreak!
The feature that makes Sn0wbreeze so appealing is the new “Baseband Preservation Mode.” This allows you to keep your current unlocked Baseband  for your iPhone, whether its 3G, 3GS, or 4G. Pretty sweet and simple.
A novelty feature with this new version is that you can play Pac-Man while your custom IPSW is being built for your iPhone, iPod, or iPad. Something worth mentioning is that it also will allow you to change your Boot Logo, although you are already able to do that by installing Boot Logo in Cydia and finding the desired Boot logo in Cydia. Or if you like photoshop you can even create your own!
Also a very noteworthy addition is that this Jailbreak also has the tweak from Comex which fixes the iBooks apps from crashing.
Supported devices:
            iPhone’s : 3G, 3GS and 4G
            iPod Touch’s : 2G, 3G, & 4G
            iPad : There’s only one, for now!