If you try to launch an application and are greeted with the message, „Not an executable,“ there are two possibilities. Either you’ve downloaded the wrong binary for your platform (e.g. you’re trying to run a PPC program on an Intel box), or you’re missing a system library.
To find out what libraries are required by an executable, open a Terminal and type:
strings EXENAME | grep lib
replacing EXENAME with the program name. This will spit back a list of required libraries. You can then search your system for the library filenames. Any that don’t turn up, you’ll have to download and install. This should clear things up. Otherwise, read the documentation carefully to see if it mentions any other required files. If not, write the program’s author and let him/her know.