If you already have a wireless router you'll need one of the xbox wireless ethernet adapters or another router flashed with DD-WRT or Tomato firmware set up as a client bridge. The xbox adapter runs up around $100 (unless they've gone down after the release of the new internal wireless systems) and a linksys wireless router (v1-4 preferably but 5 and higher can work too) can run from $20-$60 on eBay (at least it did when I did this with my xbox).