Scaling Forms to different screen resolutions

How to make my system adapting itself to the customer's screen resolution ?

Of course, there is the ScaleBy method and the like but what happens with
the MessageDlg dialogs?

Is there a way to scale them too ? Also, I have a problem with the main menu
of my Main MDI form. The character size is not scale while the character
size in my chid forms are.

Any hint would be appreciated