When you're designing the userform inside the VBE, you'll see an icon on the
toolbox toolbar that looks like an outline of a frame with xyz in the top
border. If you let your cursor linger over the icon, you'll see Frame as the
tooltip.
If you put your optionbuttons within that frame, then the buttons will act
together--click one and the other one is unselected.
Kind of like the way Tools|options|view tab has Comments distinct from Objects.
