Few months old topic, however it didn't come clear how desktop size works, or if its even possible to do these any convinient way.
My program uses this code to adjust window properly on my screen. I know it won't work for others.
What the code does is making window that is exactly from top edge to bottom - HeightOfTaskBar. On widescreen monitor i don't want to use wsMaximized, it would look stupid.
height:=screen.Height-95;
width:=height*4 div 3;
top:=0; left:=(screen.Width-Width) div 2;