In your post you talk about the "Arduino Wireless SD Shield", while the title says "WiFi Shield". The two are not the same. While the Arduino WiFi Shield is capable to connect to WiFi networks, the Arduino Wireless SD Shield is just a shield offering connections to an SD card and to an XBee module. Although you can connect WiFi capable XBee module (RN-XV, WiFi Bee or XBee S6 to name some examples) to that shield, the shield alone doesn't allow you to connect to a WiFi network.