'Listen' Server Setup Help please!

Hi, I’ve been trying to make my own gmod server. I looked into it and it turns out, I can’t host a dedicated server. So I was wondering if any of you guys knew how to set up a listen server. (One you open with create multiplayer).

I can’t find a working method to make it accessible. My router is a thomson tg787t and I’ve forwarded two of the required ports (It only let’s you forward games, and auto detects the needed ports.)
Can someone help me???

(Just to make it easier I have windows xp sp2 with pentium 4 processer, and great graphics (not sure what card), and 25gb bandwidth of adsl.)

I think if you have a router, and you get the internet through that, you can’t host a listen server.

Then why can you host dedicated servers that can?

No, you can. You just need to open the port the server is listening on which by default is 27015.

Look up port forwarding for your router and make a firewall program and port exception to allow GMod to host.

But I don’t honestly have a firewall. They usually screw up my games. So yeah anymore suggestions?

Read my tutorial : http://www.facepunch.com/showthread.php?t=887129

Have and it didn’t work for me. This is not my first attempt either.