I had the Xbox 360 wireless network adapter and gave it away. It only works with a select few wireless routers. At the time in 2008, these were all 802.11g and none were 802.11n certified.
For less money and easier setup than the $99 adapter, you can use any router to expand your existing wireless network. Then just plug your Xbox 360 directly into the 2nd wireless router. Probably the easiest router is the Apple Airport Express given its ease of use and small size, but anything should work.
Also, when you plug your Xbox 360 directly into a router, you don't have to adjust your NAT settings (don't have to call your internet provider or Xbox Live).
I hope this answers your question.