There's a program called MW2SA that you can use that works completely on the router side that interprets incoming packets and allows you to ban ip's of users through steam's web interface. I use it all the time and love the shit out of it. Seriously. If it was a girl, I'd stalk her until she court orders my ass. The only thing is that you MUST be host, but you can get host pretty easily.
It takes balls to admit that...
Weird. Every time I try to listen to my E-mails, I just hear music from Star Trek: TMP.
(With apologies to South Park)
What about apologies to Canadians? >:[
Not until they apologize for Brian Adams. Fair is fair.