The JConsole setup has two parts: a server end and a client end. The Application Server domain is installed on a machine called appserver.sun.com, which is a powerful Solaris server. This is the server end.
The client end also has an installation of Application Server. Let us assume that the client end is a Windows machine with Java SE 5.0 and Application Server installed.
The Application Server installation is needed on the client end only when your Application Server domain has security enabled on the remote machine (the default for Enterprise Edition). If you just want to administer an Application Server Platform Edition domain on the Solaris machine above, you do not need the Application Server installation on this client machine.
If the server and client ends are on the same machine, you can use localhost to specify the host name.