I only did this once and this was around 3 years ago on a ViewSonic 720p monitor, tho it should work on an old CRT. Go to x server display configuration and click advanced and change "viewportin" and "panning" to higher than the "viewportOut". Or I suppose you can just put in say 1920*1080 in your .xintrc by this medtod: add viewportin 1920 and panning to 1080. Sub the 1080p reference for what ever you like. I'm sorry if this does not work for you, its been a while.