Ok i am having a problem connecting with friends on modern warfare 2 on my xbox 360..?

i have researched and watched many videos and still cannot find the source to my problem. the friends im trying to connect to are local and with 30mi radius. i've tried port forwarding. managing dmz. my nat type is open. and still cannot connect with their games or parties. i've also tried changing my local ip from 192.168.1.1 to something like 192.168.2.1 and even to something more specific like 192.168.1.125. STILL NOTHING! the last thing i've tried is direct connecting my xbox with my IP's modem and that still wont work. it irritates me and i cannot find a solution. i use a Linksys by cisco model WRT54GS2 router that i connect my xbox to. my friends have either the same router or the WRT54G router and i've noticed that we all get the same ip from the router. could this be the problem? if not can someone help me....... up to this point i feel i've tried everything