COD 4 MP questions (Split screen etc) Advantages vs Pc?

[Kuraudo]

I don't know if I should buy Cod4 for ps3 or not, since I like the mouse + Keyboard. I borrowed my friends PC version of COD4 and beat the campaign, but now I want to buy the game on some platform, since I don't believe in piracy.

I just want to be able to play with my friend who comes here on weekends, he can't just sit and watch (that is no fun!)
Then I read you can't play Campaign and Online vs. other players.

Can you at least play deathmatch vs. the Computer?
I think friends will get bored if its just one on one.
What advantage does the PS3 ver. of COD4 have vs. the PC?
Right now I can play COD4 1920x1200, but the PS3 is half of that res.

I'll probably buy the FRAGFX but i'm still short on cash.

Going to decide today if I'm buying
A. Warhawk
B. COD4

If I still had a job, I'd be able to get both games and the frag Fx, but I can't right now. I do start work again pretty soon, but I still need to pay current bills.

Oh and thanks