Site issues should be better soon thanks to @iOPK. Windows version should be out tomorrow or the next dayIn case you don't know, GreenPois0n RC5 for Mac OS X was released yesterday bringing untethered jailbreak on iOS 4.2.1 for all devices. You can use our guide posted here to to get untethered jailbreak on iOS 4.2.1 without need of 4.2b3 SHSH blobs saved on Cydia.
GreenPois0n RC5 for windows will be out in a day or two
iPhone hacker p0sixninja, a member of Chronic Dev Team, has just announced on his twitter account that GreenPois0n RC5 for windows will be available tomorrow or the next day.