when you install a 10g database it gives you an option to install a dbconsole alone with it (on the server) . It ususally installes it on port 1158 or 5560 or something like that.(look it up in the ports file that gets created after the install) Even if it is installed on the database server, you need to make sure it's running or start it on the server (dbconsole start), then you should be able to use it.