You can change the size of the remote desktop at any time by using the OS system tools directly from within the NX session, and then via the menu you can select whether to view 1:1 or not.
For example, if you are running a virtual or a remote desktop on Ubuntu 11.04, you can change the size of the remote screen by running the ‘Monitor Preferences’ tool from the System -> Preferences -> Monitors menu. It is then up to the Player to adapt the way it displays the content of the session inside its window.