ipad 4.2.1 jailbreak problem.?

[Tim G]

ok so today i found out 4.2.1 gm came out for ipad. so i wanted to jailbreak it with redsn0w. i saw like 25 tutorial videos of the same exact thing over and over again. i followed every step, i upgrade to 4,2,1 and now, the problem is finding the ipsw file. i downloaded and ipsw file for the ipad from a popular website. and i chose it, but when i browse it in redsn0w it says it is not vaild or some crap like that. can you guys please tell me whats wrong. because the whole reason i jailbroke was to get free apps and thats also why i bought an ipad. but now it doesnt work. please help me im on windows 7