Requires Windows XP, 800MHz processor, 256MB RAM, and 10MB HDD space. You also need broadband internet.
Maximum recommended range is 30 feet/10 meters (unobstructed). My Wii is maybe fifteen feet and two rooms away and it works fine.
It plugs into a USB port and lets your DS' and Wii systems (up to five total, I believe) wirelessly connect to the internet your computer is connected to. You get this CD that installs the stuff your computer needs to run it. When you plug it in you get this little window that lets you allow or disallow systems and see what's connected and its signal strength.
Need anything else?