This assumes you have DSL or Cable, and these notes show how to configure a linksys router to run "one" computer as DMZ host. Other firewalls and routers may be slightly different but the principles are the same.
First you need your local IP address. This is not the same number as your Internet IP address.
On windows xp, open a <a href="javascript:void(0)"onClick="window.open('http://mtm2.com/~forum/images/dmzhost1.gif','win','scrollbars=no,left=100,top=100,width=365,height=325')">Command Prompt</a> and type "ipconfig" then press enter. You will see something like this (color added for emphasis):
<center><img src="http://mtm2.com/~forum/images/dmzhost2.gif" width="532" height="287"></center>
In this example, the local ip address is 192.168.1.99. It may be different for you but it will usually begin with 192 or 170 or 127, though that is by no means carved in stone. The point is that this number 'should' be your local ip address.
Next, goto your router configuration page. You can usually do this by typing
http://192.168.1.1/ in your browser's location bar. Again, that may vary depending on your particular router. Anyway, goto the <a href="javascript:void(0)"onClick="window.open('http://mtm2.com/~forum/images/dmzhost3.gif','win','scrollbars=no,left=2,top=2,width=758,height=552')">DMZ tab</a> and type in your local ip address and click apply.
That's it. Your computer is now unprotected by the router's firewall, and you should have no problem on the internet gaming zone, or in multiplayer games.
Note. The local ip address may be a different address each time you power up your computer so you might have to check to be sure the router is up to date.
Important. It is not a good idea to run as DMZ all the time. When you're finished on the zone, it's wisest to disable DMZ until next time.
Lastly, this all assumes the windows xp built in firewall has been disabled. If anybody knows how to configure the windows firewall, please feel free to add your notes below.