Make sure you have the camera selected (so that it is the item in the parameters palette) go to the object menu, select lock object. Camera will no longer move, until you unlock it. If you mean the preview window itself (so you don't accidentally drag it) click the little down arrow in the right corner of the window, and disable drag docking. That will lock the window in place.

--------------------------------------------------------------------------------

Consider me insane if you wish, but is your reality any better?