this is the wrong area of the forum. Everyone gets confused thinking jailbreaking is something you do to the OS. The jailbreak is an altered firmware/OS that has been altered to enable you to run 3rd party apps not sanctioned by Apple. So you can't jailbreak unless there is a jailbreak for 4.0.1 available. Anyway just read there is one out for pwnage tool but only for 3Gs with old bootroms if you have a new bootrom there is a new tool soon to be released you'll have to wait for that. If you don't know which bootrom you have search for threads I've created I have a thread where I put info on finding your bootrom version.