All commands must be done with sudo privileges:
You can enable remote management with the these commands in command line. This is very useful after you have created a hidden admin user, because the GUI will not allow you to see the hidden user in the sharing preference pane. Its also very useful for scripting. I made a script that creates a hidden admin user and performs this configuration, and I rolled it into an OSX installer packager. Then I carry it around on my USB stick for any machines in my area that are not accepting ARD connections.