OK so seven thousand people looked at this in six months so it must be worth a few lines of advice.
Settings>Wireless and networks>Wi-Fi Settings>Select your network by the name of your router's SSID, click to connect then enter your wireless security key and away you go.
If you need to know how to find the SSID and security key, read this Sticky Post http://www.tomshardware.co.uk/forum/38111-18-find-change-wireless-security