I can't, but you might be able to and if you can't you could probably get a patch somewhere.

Yeah, it seems like a rip-off of L4D to me though. Plus none of the mutants are wearing pants O_o

Actually it's not a rip-off of L4D. Quite the opposite, Killing Floor is an Unreal tournament mode that was developed into a game I think. Unreal tournament was released long before L4D.

I still think Left 4 Dead is the better one though. Better graphics and gameplay all in all imo. KF could use some more graphic work. Just my opinion...