Well there are work arounds yes and I actually use one on my 360 on the bedroom. however that type of work around would require you'r 360 to be withing 6 feet of your PC and for your wireless adapted to also have an ethernet port. Even then I'm not sure what kind latency issues there are in MP games. I'll assume your 360 isn't close to your pc.

You can always get a longer ethernet cable from monoprice.com for pretty cheap. From what I've read over the life of the 360 the first best bet for a wireless adapter is the one by MS, all 3rd party adapters are hit or miss at best. Now with all the new 360s coming out have wireless built in so the MS wireless is in the process of being discontinued. So $50 for the dual band adapter probably not to bad but a longer ethernet cord would most definately be cheaper me thinks.