If i buy a vBulletin owned license from a friend. Is that against the rules. And Can I still make my own Login name for the forums and stuff. Could I change the contact details to mine rather then his?
Yes it goes by the email address of the license holder, so if it's transferred in to your name, and the license is current you'll be able to make an account AFAIK. His account would then show up as unlicensed.
It is always best to ask over at vBulletin.com for licensing questions, that way you can get confirmation from the official vBulletin support team or at least there they are able to check any replies made by others to ensure that you are given the correct information.