os loader for osx (tiger).sit doesnt install on my macHELP!!

i've downloaded the os loader for updating my os on my mpc 4000 but when i try to launch the macosloader.sit it tells me i have to pic a programm to launch it caus it doesnt know which programm it needs....
does anyone know what to do?????

The ".sit" in that file's name is the extension for Stuffit Expander. You need Stuffit Expander to decompress the ".sit" file which contains the desired OS Loader... perhaps you do not have it (Stuffit) installed on your computer. If you do have it installed and don't know where it is... it should be in your "Utilities" folder... which is located within your Applications folder. If anything, use Spotlight to find it... or download it from the link i provided.