From Apple Sales Web...
AirPort Extreme Base Station Shipping, 802.11 Enabler Available
Apple is now shipping the new AirPort Extreme Base Station that is
based on 802.11n wireless technology and is compatible with 802.11a,
802.11b, and 802.11g wireless networks. During the past several
months, Apple has shipped some Macintosh computers with the hardware
needed for 802.11n. See below for eligible systems.
Customers who buy the new AirPort Extreme Base Station will receive
the software that enables 802.11n functionality on these computers at
no extra charge. For customers with eligible computers who wish to
enable 802.11n functionality but do not wish to buy the new AirPort
Extreme Base Station, Apple has made make the 802.11n Enabler software
available for download from the Apple Store online for a nominal fee
of $1.99.
The following Macintosh computers have the necessary hardware for 802.11n:
MacBook Pro with Intel Core 2 Duo
MacBook with Intel Core 2 Duo
Mac Pro with Intel Xeon and AirPort Extreme
iMac with Intel Core 2 Duo (except iMac 17-inch, 1.83GHz)
.