My friend has had constant issues with his wireless network using his dated Linksys router. So he finally decided to upgrade to the Netgear N750. It's a dual band router that simultaneously broadcasts 2.4 and 5 GHz bands. He setup the 2.4 band for the laptops and mobile devices to access, and the 5 band just for gaming on his xbox 360 Slim. He immediately ran into a problem. The 360 slim's built-in wireless card only picks up 2.4 GHz frequencies. To remedy this, he purchased Microsoft's xbox 360 wireless-N adapter as it can pick up 5 GHz frequencies. However, there was no change after plugging the adapter into the 360 slim. His HP laptop can see the 5 GHz network just fine, so we know it's being broadcast. Could it be the xbox is out of range of the 5 GHz band? Is the adapter not functioning properly with the 360 slim? Any troubleshooting tips would be greatly appreciated.
I guess he could test the distance theory pretty simply. Take the laptop where the Xbox is and see if he can get a signal. Or get a TV and plug it and the Xbox in closer to the router. Personally i have never used the "official" Xbox adapter (i used a Linksys WGA54G which worked perfectly from about 100 feet from my Linksys WRT54G router) so i don't know what type of range it has. From everything i read the range on them is great.
You also may want to check the type of encryption used on the router (if he used it which he should) because that adapter has support for WPA2, so i have no idea if it is compatible with other types like WEP.
This is part of an article about setting one up:
"The Xbox 360 Wireless N Networking Adapter works much the same as the original wireless networking adapter did. Simply hook the adapter into the two divots on the back of the console, and plug in the USB cable. The 802.11n-compatible accessory uses two adjustable antennas instead of one. They should be angled to ensure the best possible signal; a V-shape is usually preferred. The USB cable protrudes out of the top of the adapter rather than the side, so it might be visible from your couch.
Once connected, configuration is simply a matter of heading to system settings on the console and finding your network. The Wireless N Networking Adapter will pick up 802.11a/b/g and n networks and provide a signal strength meter for each. You can input your network's password or use Windows Connect Now (WCN) setup if your router supports it. Using the standard controller to input a password can be time consuming. The Xbox 360 will remember your last used network and password between shutdowns and even when switching adaptors. It can't remember multiple networks, though, and this is a frustrating omission if you're regularly switching between two or more Wi-Fi networks.
Once configured, we easily connected to two 802.11n networks at a distance of 20m; one operated on the 2.4GHz radio frequency, while the other worked over 5GHz. Over both networks, streaming 720p media was flawless. However, we noticed little to no difference between the Wireless N Networking Adapter and the original accessory with Internet-based activity; both passed the Zune Video Marketplace's 1080p HD streaming test and downloaded a 66MB video in the same time.
If you don't yet own a Wi-Fi adapter for your Xbox 360, Microsoft's Wireless N networking adapter is an expensive but worthwhile purchase for wire-free gaming and media streaming. Those who own the original wireless adapter only need consider it if they are having problems with signal strength."