Unusual problems trying to host game server

Hi,
I'm trying to host a game server for Need For Speed Hot Pursuit 2, and I am having problems, even though I have forwarded the ports on my router and enabled DMZ. I am using the D-link DI-524 router. When I try to host, I don't get the message in the game saying I failed to connect, but the server isn't displaying on the public game list. Someone can join, however from the private game option, by entering my public IP, but something is blocking it from being on the public list. I have tried one site to see if the port was actually open, and the site said it could see my service on TCP 8511 (main host port for the game.)
The server works when I make a direct connection to the modem (not using the router at all then), but then the other PCs relying on the Internet can't use Internet while I host then. So I'm trying to find a way to host with the router.
I've tried so much, disabling my software firewalls and leaving the ports open there, changing over from a dynamic IP address to a static, and even tried a setup with port triggering, but everything fails.
Someone has loaned me for a few days, and the server works with it. So I know it's something with the DI-524 that it's blocking the server from listing. Could the problem be that it won't display from too low horsepower?
Can someone help me with what to do?

Thanks, Jason

Jason08