I did come accross some code which auto sized the form based on the screen resolution. I think it was in Litwin / Getz / A.N Other's Access Developer handbook(s). It seemed inordiantely complex. I think it resized every control and every font to keep the design consistent, seemed to work but took up a fair bit of processing.
I try to design for 800x600 for sub forms, as being the lowest common denominator these days.