I was at Wal-mart last night and found a Belkin wireless bridge for the xbox 360 for $60. I took it home, set it up on one of my PC's and plugged it into the xbox. Worked like a charm. I'm now online, part of xbox live and have my media center and xbox talking to each other.
I absolutely love how you can download demos of games and download other things like movies and themes and stuff. Its not all free, but a lot of it is. The media center integration is going to be very nice too. I highly recommend the belkin bridge over the Microsoft one for price alone since its $40 less.