I had never had any problems with my NAT settings until I attempted to host last Wednesday night. For some reason my NAT setting went from open to moderate. I tried everything with the router(Linksys WRT54GS), DMZ, forwarding ports, Static IP on the 360, etc. but nothing would move the NAT to open. Finally, I placed everything back into their original settings and I unplugged the router for 30 seconds or so to make sure everything reset correctly. Guess what? The NAT settings turned to Open. No idea why things got screwed up, but that seemed to work for me.