You may want to add some detail to bug #1459 or better still create a new bug as this is a slightly different problem affecting the same class of device - is there more than one Apple 11n access point available?

Kalle Valo (the Nokia WiFi firmware developer) is attempting to investigate issues with the Apple access point(s) though I'm not sure which model he plans on purchasing. If you can provide more details concerning your issue, he may be able to investigate further and get to the bottom of the problem - it could be a problem with the N800 firmware, or an Apple problem, or a combination of both however the N800 does sound like it's the culprit if the other Macs and Wii don't cause a problem.