There is a known issue with the Intel 4965agn Wireless Adapter...

Intel recommends using security with your wireless network. The Intel(R) Wireless WiFi Link 4965AGN adapter can only achieve transfer rates greater than 54 Mbps on 802.11n connections when using AES security, or no security. You should only use no security when setting up or troubleshooting the network.

Also the Intel My WiFi PAN will operate over the 5.2 GHz band (802.11a) only when the Intel My WiFi STA station is connected to an access point that is operating over channel 36, 40, 44, or 48 (5.2 GHz)...

LGM,

I gotta throw my 2 cent at ya and save you some troubles. I had the same thing going on with my POS laptop. I recently purchased the 400N in hopes that it would be all I needed to do in order to go "N". ...wrong.

I had to go back to the store and get the network adapter. I came to terms that my onboard Intel wireless adapter wasn't going to cut it in the "N" world.So theres that...

Also, as far as the software that came bundled with it, forget it, its garbage.  I downloaded the "setup wizard" file. Not the CD Image. It basically installs the router so that you can install it and log into it and make changes through 192.168.1.1. Way easier...

Now, this interface is different than previous versions. Some options are hidden in order to make things "easier" or default if you will. A big pain in the **bleep** if you ask me... but since you have two bands at your disposal, it helps to name them to be able to tell which one you are connecting / connected to.

Once you get there, you want to go to: Wireless - Basic Wireless Settings. Choose "MANUAL" settings and from there you will be able to name and choose the settings for both 2.4Ghz and 5Ghz. Once they are named, you'll see them both under connections available in Windows. Its wierd to see but, you paid for two bands...its your world now.  I named mine with a "24" in one and a "5" in the other so I always know.

Anyway, if your laptop still can't see the 5Ghz  you might have to go get a USB adapter as well. I have 3 laptops in my house and only 2  see the 5Ghz band without the need for an adapter. The other I had to buy the WUSB400N and it was sweet sailing after that. Picked up the 5Ghz no problem. Hope this helps!

...don't always claim to be a "techy", but I'll give ya what I think I know...

Just to clarify a point in saber_tooth's reply: strictly speaking, there isn't an issue with 802.11n security and the 4965agn per se. The 802.11n draft 2.0 standard requires WPA2 with AES if you're going to run crypto. It's all or nothing when it comes to security and wireless-n's higher speeds. You can either run your access point with no crypto (unsecured) or, if you choose to encrypt your wireless connection, you must use WPA2 with the AES algorithm or your router/AP will fall back to 54Mbps.

*edited to correct a typo* 

Another point: