Yes!
1. Download a game on the internet, PS3ISO.com is a really good website for downloading games (Usually the game you download will be in several parts or if it's a torrent download, it'll be one file)

2. Extract the game if it's in a .rar file using winrar or a similar program that can extract a .rar file.

3. Then in that folder that will be called the region code then the game name e.g. BLES01031 [Call of Duty Black Ops]. In that will be 3 files, called: PS3_GAME, PS3_UPDATE AND PS3_DISC.

4. Put the folder with the region code and the game name in a folder called "GAMES" or GAMEZ" on a USB or an External HardDrive

5. Go to your PS3 and load multiman, go under "games" tab and your game will be there

have fun

Ohh man you HAVE to have a jailbreak, firmware 3.55 or lower