Apple's much-anticipated software update that enables the AirPort Extreme cards in some models of Intel-based Macs to support the new 802.11n standard, which is faster and supports a wider range than the previous 802.11b and 802.11g standards, is now available for purchase from Apple's online store. The update costs $1.99 and is delivered via immediate download.
The update is compatible with the following Mac models:
MacBook with Intel Core Duo 2
MacBook Pro with Intel Core Duo 2
Mac Pro with AirPort Extreme option
iMac with Intel Core 2 Duo (except the 17-inch, 1.83GHz iMac)
If your Mac supports 802.11n but didn't come with it already enabled, head over to The Apple Store to purchase the software or read more info about whether you need the update.