i have an iphone 4, i would like to jailbreak it but it has 4.2.1, i need help on where i can jailbreak it, i DONT have a mac and ONLY have a Windows XP Computer, i have no idea how to jailbreak it, it has never been jailbroken and if someone could link a video on how to do it maybe... thanks, oh and i have tried greenpois0n but it did nothing, i dont know how to get it to jailbreak so i need help...

thanks