The link by @mikewhatever is correct. But basically you have to use the Help Question Mark icon in the remote login box first to set up your remote link(s). This opens Firefox in a guest session but it takes you directly to the login (use your Ubuntu One credentials) after which you can set up the settings needed to RDP to another machine. When you're all done, log out and close Firefox. You'll then be taken back to the computer's login screen where you can choose the Remote Login, use your Ubuntu One credentials to log in, and this time you'll see the RDP client(s) you set up earlier. Log in to your chosen machine. After that, any Ubuntu 12.10 machine you use in this way will let you log in to any of the remote machines you set up earlier without having to log in to the local machine because the RDP settings are stored on Ubuntu's servers.