The Chronic Dev-Team has recently announced via twitter that they will release their Greenpois0n untethered jailbreak for Windows this weekend.

Site issues should be better soon thanks to @iOPK. Windows version should be out tomorrow or the next day

greenpois0n windows Greenpois0n for Windows will Be released this weekend

Greenpois0n for Mac OS X with support of iOS 4.2.1 untethered jailbreak was released yesterday.