thanks for the quick answer. It seems that you have a newer airport extreme than I have. Mine does not support the N-draft and has an Atheros chipset and not a Broadcom one. Therefore, I would conclude that my problem is chipset related.
Thats interesting, when did you get your Mac Pro?
Did you special order the Mac Pro with the WiFi and Bluetooth cards from Apple, or was it upgraded later?
I pre-ordered my Mac Pro but had it replaced after a week or so, with the replacement being delivered around 13th September 2006 (give or take a few days).
As for 802.11n, all Mac Pros with WiFi cards from Apple should have that. It is just that the very first ones (including mine) were sold as only supporting 802.11a/b/g. It was later on that Apple let you buy a software unlock (http://support.apple.com/kb/ht2447) to enable 802.11n on these early machines.
I wonder whether anyone else on here can confirm which Apple wireless cards their Mac Pro came with.