Instructions
Turn on your PS3 and select the "Network Settings" menu option under the "Settings" category.
Select "Internet Connection Settings" followed by "Yes" to confirm your choice and open the network configuration menu. You will be disconnected from the Internet at this point.
Select the "Custom" option, then choose "Wireless" when prompted to specify your connection type.
Select the "Scan" option and wait while your PS3 detects any nearby wireless networks.
Select the network you wish to connect to, then select the "WPA-PSK / WPA2-PSK" option when asked to specify the encryption type present on the network.
Enter the encryption key in the next screen. It will be shown on your monitor as a series of asterisks, so make sure you input it correctly.