Hard Mac has put an 802.11n Mac Pro card in a Core Duo MacBook. The task involves removing several screws and the keyboard from you MacBook but it does work. Its amazing that the MacPro and the MacBooks are using if not the same, then extremely similar Airport cards.
I’m actually considering this because I am in the market for a new Router and the Airport Extreme looks very appealing to me, but I don’t have 802.11n in my notebook now I can hack myself 802.11n and get the greater throughput of N.
Check out there little step by step guide here.