Heres what you can do, go find yourself a cheapo 802.11g access point and set it up in client/bridge mode, then connect it to your 360 via a short Cat5e. G band is plenty fast enough for streaming content and online play. the only reason you should buy a top of the line N adapter is if you need massive amounts of lan throughput. the thing most people dont realise is that gigabit lan in itself may be fast, but streaming video and big file transfers will only go as fast as your hard drive, which is nowhere near gigabit speeds.
And before you pull out the Sata 3Gb/s argument (i've heard it many times), 3Gb/s is the speed of the Bus not the Drive.