Russ,
Use the AutoShape Arc, it's in the basic shapes category.
Press Shift and hold, click and drag with the mouse to create a quarter
circle. Adjust the size at will. Let go of the mouse and then the shift key.
Now there are two diamond shaped adjustment shapes, drag them to get a
perfect demi-circle. To get it completely right you can draw a line next to
the circle or use the guide lines.
Luc