The standalone version, is JBoss with just the Naming and JBossMQ services running.
So the only real advantage of the standalone version is that it has a smaller memory footprint since it does not have all the services running.
If you want to use it with another JBoss server on the same machine you would have to make sure you do not get a port conflict since both servers would try to start the naming service (Disable one of ther Naming services or change the port number of one of them).
Gotcha - thanx. This was made clear after I downloaded and tried it :-)