Unable to Host a Game Troubleshooting Checklist
How to configure your computer and network gear to host games online
If your network has a router that connects to you to your ISP equipment verify these 2 things.
1. UPnP has to be enabled on your router.
2. Port 6112 has been redirected to your IP address for TCP/UDP traffic.
Windows XP has 2 services that are required for UPnP that are set to manual by default.
1. Verify that the service "SSDP Discovery Service" is started and set to automatic.
2. Verify that the service "Universal Plug and Play Device Host" is started and set to automatic.
Additional Resources:
Microsoft’s information about of UPnP
D-Link walk thru enabling UPnP services for Windows XP