Do you know how to develop a FM solution to look great at least at 640x480 and 800x600 variable screen sizes? Do you know any plug-in to automatically detect the final user screen resolution and center the layouts or go to a specially designed layout?

if you don't have too many layouts, you could draw two sets of layouts, one for 640 and another for 800. Then for any scripts that change layouts, add a step that checks the screen resolution (using status(currentscreenwidth)) to navigate to the correct layout.

This should work, but it will get old fast if you have many layouts, plus beware when you are developing, any changes to one layout must be made to the other one too!