Is it Vista or my internet connection?

[sur3nd3r]

A week ago I reinstalled vista on my dell xps 420 which I primarily use for gaming. I reinstalled all the proper drivers and etc. My internet works perfectly with internet explorer and other programs like AIM. However, I haven't been able to connect to any online multiplayer server, for instance call of duty 4 or counterstrike. I will simply get stuck on the loading screen and ultimately get a "connection timed out". I have tried reinstalling network drivers, tinkering with connection settings, power cycling my modem, computer restarts, system restores, firewall settings, and yet I can't get it to work. I asked my "tech" friend to help me out and he too couldnt get it to work. Being a mac user he blamed my vista and said its probably some bs setting thats screwing it up. At first i didn't buy it, but now after days of frustration and trying everything I've read online about such issues I'm leading towards vista being the problem.

Can someone! ANYONE! HELP A GAMER IN NEED!