Instructions
Right-click the video file on your computer that you want to play on the PS3. Click the right mouse button and select "Copy" from the menu that appears.
Plug the USB thumb drive into the computer. Click the "Start" button, then click on "My Computer" and double-click the USB drive's folder. The USB folder will load; click the right mouse button on any blank space inside the folder and select "Paste." Wait for the file to transfer to the USB drive.
Plug the USB drive into the PS3. Navigate to the "Video" menu and select the USB player. A menu appears with the files on the USB drive; select the video file you want to watch and press "Play."