Its here finally ! Chronic Dev Team has released Windows version of GreenPois0n iOS 4.2.1 untethered jailbreak for iPhone, iPad and iPod touch. And just like the Mac version, Windows version is compatible with iPhone 4, 3GS, iPod touch 4G/3G/2G and iPad.
Instructions for jailbreaking iOS 4.2.1 untethered on Windows are exactly same as the Mac version. Simply follow our detailed step by step instructions posted here to jailbreak all iOS devices on 4.2.1, untethered using GreenPois0n.