Arduino Wifi Shield Help!!

I have just purchased the arduino wifi shield. I followed all the instruction from http://arduino.cc/en/Guide/ArduinoWiFiShield#toc1

Im trying to scan the available network using these code:
#include <SPI.h>
#include <WiFi.h>

void setup() {
// initialize serial and wait for the port to open:
Serial.begin(9600);
while(!Serial) ;

// attempt to connect using WEP encryption:
Serial.println(“Initializing Wifi…”);
printMacAddress();

// scan for existing networks:
Serial.println(“Scanning available networks…”);
listNetworks();
}

void loop() {
delay(10000);
// scan for existing networks:
Serial.println(“Scanning available networks…”);
listNetworks();
}

void printMacAddress() {
// the MAC address of your Wifi shield
byte mac[6];

// print your MAC address:
WiFi.macAddress(mac);
Serial.print(“MAC: “);
Serial.print(mac[5],HEX);
Serial.print(”:”);
Serial.print(mac[4],HEX);
Serial.print(":");
Serial.print(mac[3],HEX);
Serial.print(":");
Serial.print(mac[2],HEX);
Serial.print(":");
Serial.print(mac[1],HEX);
Serial.print(":");
Serial.println(mac[0],HEX);
}

void listNetworks() {
// scan for nearby networks:
Serial.println("** Scan Networks **");
byte numSsid = WiFi.scanNetworks();

// print the list of networks seen:
Serial.print(“number of available networks:”);
Serial.println(numSsid);

// print the network number and name for each network found:
for (int thisNet = 0; thisNet<numSsid; thisNet++) {
Serial.print(thisNet);
Serial.print(") “);
Serial.print(WiFi.SSID(thisNet));
Serial.print(”\tSignal: “);
Serial.print(WiFi.RSSI(thisNet));
Serial.print(” dBm");
Serial.print("\tEncryption: ");
Serial.println(WiFi.encryptionType(thisNet));
}
}

However, the result shown in serial monitor is always changing (unstable). The signal is around -70+
My home is using WPA2 personal secuirity. What is the max range the wifi shield can support up to? Can it support WPA Personal?