Thank you - just after I asked that question I found the tutorial. What happened? I set up three outputs (1440 x 900; 1280x800; and 1024x768).
The original campaign was built on 1440x900. It runs smoothly. The other two screens... not so well. In a CRT display (1024 x 768), almost a third is cut, on the horizontal axis.
In a LCD display the 1280x800 ran well.
I checked everithing and, apparently, there is nothing else to do.
What can I do now?