Have four buttons on project title page,---all round ones found in DVDA.
But when I apply image mask overlay it doesn't take,----I get a rectangle spilling onto the other buttons.
Any thoughts?
Select your button and look in the Properties area for "Highlight"
Under "style" there are several different options (the default is rectangle, I believe). Change these options and you'll see cool stuff happen. If you use a psd, you can even use layers as custom highlight masks.