you could treat this like any negotiation. Try to understand what his interests/motivations are, and have a guess at what his walk away situation is... and at the same time work out what your interests/motivations are. Then combined with a few of the standards, you can work out options... and then put them to him in a nice calm manner.
ie.. your interests - have fun, have a consistent set of rules for everybody (that is 3.5), have a positive gaming relationship with your players.
his interests - feeling important or special, maintaining some form of power (if he has joined a group of people who he doesn't really know, he may be feeling intimidated and reverting to behaviours that make him feel secure)
your alternatives - boot him, find a new player, never talk to him again.
his alternatives - find a new group that plays the old system
standards - game system is 3.5. The group has the books even if he doesn't.
options - the group changes to the old system.
he accepts the fact that the rules are 3.5 and plays
he doesn't accept the fact the rules are 3.5, shuts up, and plays anyway with the knowledge that not knowing the rules means he has no option to argue about them.
This sounds like he has some self-esteem issues which could lead to many different behaviours... or he is just a..... (insert appropriate word here).
D.