This seems to be a common problem but whatever I try doesn't seem to help. I can connect to XBOX Live but my connection is slow (downloads and such) and I keep seeing it complain about my moderate NAT.
I have the Linksys E1000 router with a **** TM722 modem (provided by ISP).
I've tried opening my NAT on my routers configuration and allowing UPnP. I have tried port forwarding but I don't understand it at all so I might have screwed up there.
If anyone has anything they can offer, it would be greatly appreciated.
(NOTE: I was thinking of upgrading the wireless adapter on my 360 to the newer "wireless N" one to try and fix this problem)