It looks to me like the Wii already has wifi support built in. So all you'd need is a wireless router. Pretty much any a/b/g/n router should work. At which point just remember a few of the basic security rules... WEP is worthless, WPA is better, WPA2 is better still if the Wii supports it. Make sure the wireless connection password isn't something easy to guess, and has at least some character like you might find above the numbers on your keyboard.