Cannot install downloaded app files
 

Maybe someone here can help a mac-newbie. I used a pc (well i own a mac since the yesterday) to download several sit-files, copied them on a cd and started up my mac. I can extract the sit-files and most of the time then I have a file called [program-name installer.]
If I doubleclick that file to install the software no application is assigned to that file. What am I doing wrong? Can I throw away most of the files I downloaded (ex. illu 68mb)

thanks for your help!

Don't unstuff the .sit files on PC. Wintel does not understand the double fork (data & Resource) architecture of Mac application files.
Use StuffIt Expander on the Mac to open them with drag and drop if necessary.