unopenable downloads from LW either in OS9 and OSX

Yes you are not alone and I am just a beginner myself. I am OK with mp3 but .sit and .dmg will not open in either sys.

OS 922
osx151
G4 400 mhz lots of disk space
stuffit expander 6.0 (normal) osx
or stuffit deluxe 5.5 (os9)

files go in the saved folder but will not open
they even lose their icon.

I tricked a .sit file, adding what i believed was a closing sentence from another .sit file.

I got the icon back but it says that my file is not compressed and goes no further