Need to know what ip to use for modem to open ports

Hello,
I need to open ports for my games since i cant host (any game) or join a lot of servers. I want to dmz my modem, then just forward the ports from my router to my pc.

Here is the manual to do that to my modem.

http://www.myembarq.com/files/emba [...] arding.php

On the last step (19) it says i need to
19.To DMZ a device on the network. Enter its static LAN ip in the line 1 "All Ports" field. Click Save

But what ip do i use?

Also if i do this then will i be able to host games after forwarding the ports through my router?

I have tried connecting my pc directly to the modem before, with no help.

That is why i know it has something to do with the modem.

Any help would be great.

What is that and how do you do that?

Ok yeah i am going to later. Thanks for the info.