Instructions
Select the PSN Store icon on the PS3 main menu to open the PSN Store application.
Select "Add-ons" and "Disk Based Add-ons" to bring up the PS3 system add-ons. Browse through the list until you see the "PS2 System Data." Select it.
Select "Add to Cart" and "Checkout" to begin downloading the PS2 system data for the PS3. This is a free add-on, so you do not need to enter in any purchasing information.
Go back into the PS3 main menu and insert your PS2 disk into the PS3 optical drive. Go to the "Game" section of the PS3 and select the "PlayStation 2 Format Disk" to begin playing.