I had exactly that problem with my new N800 and my D-Link DIR-422 802.11n router. My N800 couldn't even see my wireless network unless I walked a couple of houses down the street.

My Windows XP laptop had a similar problem, even though an Ubuntu 7.10 liveCD booted on the same laptop connected instantly. That hinted at a software issue.

I switch the XP wireless software on the laptop from the laptop vendor's to the native XP stack, and it connected. That encouraged me to upgrade my N800 to OS2008, and it also connected flawlessly. Joy!

Please give OS2008 a try. It solved this problem for me. And please let me know what happens.