Just got this game, would love some co-op!

[Easter Bunny 00]

Hey! I just rented this game, and had no clue that this had co-op! If anybody wants to play together, or if anybody is kind enough to help me level my guys up, id really appreciate it

Also, is there a difference in the exp you get via difficulty? As in do i get the same amount of exp from killing an enemy on easy as to killing an enemy on hard?

And, I know there are 5 campaigns. About how many levels are in each campaign? Im just curious, i want to pace myself so ill have this maxed out when Portal 2 comes out

Any help is greatly appreciated. Thanks you guys

Btw, if you do want to help me level up or play co-op, send me a FR - GT: Easter Bunny 00 (zero's, not O's)

Thanks again