Instructions
Scroll over to the "Game" menu on the home screen of your PS3.
Scroll down to the folder containing PS1 games that you have downloaded onto your PS3. Press the "X" button to open the folder.
Select the PS1 game that you wish to play and press the "X" button.
Press the "PS" button located in the center of the PS3 controller once the PS1 game has loaded.
Scroll down to the "Other Settings" option, on the menu screen and press "X."
Press "X" on the "Screen Mode" option to alter the fit of the game on your television screen. The "Normal" option keeps it sized for a standard 4:3 television. Selecting "Full Screen" blows up the image to fit a widescreen monitor. Press "O" to exit.
Press "X" on the "Smoothing" option and choose "On" to smooth the graphics of the PS1 game. This creates a noticeable blur in the game's graphics, but it decreases the jagged edges that are common in PS1 games. Press "O" to exit.