open command line
tar -xvf thefileisentyou in directory it is in
this extracts .sit file
then run stuffit on that
adobes opening, trying to open it, because the mime type is set for that program, it wouldnt work anyway doing that, do what i said above
you're not actually running any files so theres no danger, people who say stuff like this are retarded, the files arent even chmodded to be executable
if you cant manage the command line then navigate to the download in one window then open your program you generally use to extract files, drag the tar.gz file into the program, i think on a mac that should work