AceInstall

When you download ACE, you can typically expand the archive by simply double clicking on it.

When you download the corresponding ERG image, you might not be able to automatically extract that if your system isn't configured to recognize the bz2 extension.

Open the Terminal application (use the Search (looking glass icon in the upper right corner) option to find it).

Note where you put the ERG bz2 file. Let's say it is on your Desktop. Navigate to that directory, i.e., in the Terminal, type:

cd ~/Desktop

Then call the proper utility directly to expand the archive:

bunzip2 erg-1212-osx-0.9.22.dat.bz2

Now hopefully you have the ERG image to test ACE on.

Navigate to the directory that you put ACE in:

cd ~/Desktop/ace-0.9-22

Now you can start ACE:

./ace -g ~/Desktop/erg-1212-osx-0.9.22.dat