Can't connect to host on same router

[rev4]

Alright, this is my last resort.
My brother and I recently bought cod5 so we both have 2 copies.
We're trying to play Nazi Zombies but we are having problems connecting to eachother.
The problem is, whenever one of us tries to host an online game, it wont let us connect. We have a friend that can connect to either one of us when we host, so we know we can host.
My brother and I are on the same network so we figured thats the problem. We tried disabling punk buster but the problem still exists.

Oh, and if i were to join an online host, and my brother were to join, it would kick me off and he would be on it. and vice versa.

Any ideas? D:!

[FunkY]

To setup for multiple users:
1) Right-click on the Call of Duty 4 icon you use to start the game.
2) Select Properties.
3) In the Target field you'll see a line like "C:/Program Files/Activision/Call of Duty 4 - Modern Warfare/iw3mp.exe", add the net_port command to specify a unique communication port for each system. The complete field should look like this:

"C:/Program Files/Activision/Call of Duty 4 - Modern Warfare/iw3mp.exe" +set net_port 28960

4) Click OK.
5) Repeat for each system behind the NAT, adding one to the net_port selected (28961,28962,28963 etc.. )Above's actually for CoD4, but it's the same fix: Replace iw3mp.exe with codwaw.exe for co-op/zombies, and codwawmp.exe for multiplayer.

You can re-enable punkbuster now ;)