so beyond over trying to deal with IOS.4.0.1

ive been working on this for a couple of days... there is a very easy way to revert your phone back to 3.1.3... it just doesnt seem to work on any of the phones im trying to do it on. ive watched videos on you tube of people doing it step by step and having it work but it isnt working on my phones it doess everything the same but when you select the firmware version it simply tells me its not valid...