This works for the Xbox 360, Xbox and PS2 to connect your machine to your wireless router.  There are some great reviews on this thing over at Amazon...

Regularly retails for $49.99, grab it for only $19.99 (instead of the $99.99 Microsoft adapter). 

Click here for this deal:  $19.99 Linksys Wireless B Game Adapter Special

Some product details:

The LINKSYS WGA11B Wireless-B Game Adapter gives any wired Ethernet equipped game console wireless connection capability. If you have an existing home wireless network with a cable or DSL Internet connection, the Game Adapter lets your PlayStation, XBOX, or GameCube attach to the network so you can get into online games without running wires to the game room. Or, you can use a pair of Game Adapters to form a "cable-less cable" between two game consoles for head-to-head gaming -- in the same room, or all the way across the house!

Good review info:

This is only an 802.11b, not g, device, but that is NOT a negative. Don't spend the extra money on "g" ANYTHING. b gives you 11 Mbit/sec, and if you're really lucky these days, your DSL or cable modem internet connection will get you 2 Mbit/sec. So why pay extra money for g? Even if you are far from your wireless access point, and the speed drops to only 2 Mbit/sec, you'll never use that through the internet. Your Xbox will never come anywhere near saturating an 802.11b link. I've sniffed the packet traffic, and it doesn't even break 120Kbps at its worst.