If you can't wait to get it included with your new Airport Extreme, you can now purchase the Apple 802.11n enabler for the following machines:
- MacBook Pro with Intel Core 2 Duo
- MacBook with Intel Core 2 Duo
- Mac Pro with AirPort Extreme option
- iMac with Intel Core 2 Duo (except the 17-inch, 1.83GHz iMac)
The price is $1.99 and the site does show you how to check to ensure that you don't already have the enabler before you drop money on something you don't need although if you've had your qualifying machine for a few months, chances are good that you need the enabler.