In your apps folder there should be another folder called utilities, in there is a program called network utility.
start that, then change the drop down menu that says "network interface (en0) to (en1). In that screen down the bottom of the window there will be some text that says something like (802.11 a/b/g/n)
If this says (802.11 a/b/g/) then you dont have 802.11n
o ones bearbo you beat me while i was typing 😛