How do i change the NAT type on my belkin f5d8233-4v3?

xbox live wont let me play halo 3 with my friend and when i play gta4 it says "disconnected from session returning to single player". it wont work because my NAT type needs to be set to open. i already put in ports 88 UDP 3074 UDP and 3074 TCP in on my router setup and it still doesn't work.If anyone could help it would be greatly appreciated