Instructions
If you are planning on using a wired connection, plug in the Ethernet cable to jack at the back of the PS3 while the console is off.
On the PS3's main menu, known as the XMB, go to Settings->Network Settings->Internet Connections and select enabled.
Navigate to Settings->Network Settings->Internet Connection Settings and select "Yes," as you currently have no connection.
Select "Custom," then select your connection type, wireless or wired.
On any further selection screens, select "Automatic" as the system should be able to identify the proper settings. Note that you will need any encryption keys you may have for a wireless connection.
On the next screen, press "X" to test the connection and verify that your PS3 is networked. The test can take a minute or so.