It souds to me like you have downloaded and installed JBoss on your mac. (If you ran the installer and followed the prompts like you said).
So what next... Start it up and check that it works.
You don't need ant unless you are planning on using it to do your builds. You are probably going to need it if you plan on writing any applications to run on JBoss though since it is a handy build system.
It is good to see another OS X.
Give me a shout of you need any help.