What you need:
1) Download it from above to your desktop.
2) Create a folder anywhere on your Desktop like this; /PS3/otheros (If you don't know how to do it, just create a folder named PS3 and inside it make another folder called otheros).
Note: If you want to do it on a linux system you can open a terminal and type in:
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3) You are going to put Petitboot in the otheros folder.
4) Next, move that folder into a mass storage device or burn it to a CD and plug it in the PS3.
5) Go to Settings -> System Settings -> Install Other OS, and then it should be detected on the mass storage device or CD.
6) Select the Other OS as the Default OS.
7) There you go! You should see a GUI with a little HDD icon on the left after you choose the Other OS as the default. Click on it, and then click on your linux partition. It's handy because you get your video options at the bottom plus you can return to the Game OS without typing anything in.