You can probbaly do that with PowerPoint's drawing tools - but it is really
easier to do that in a drawing program like CorelDRAW, Illustrator or
Freehand. Microsoft also has a drawing program called Expression that's
available for free download - unfortunately, that's only for the Mac now:
I had the same problem recently. A friend made this image in Illustrator for
me and I converted it to a WMF file. You can download the 2-circle- and
3-circle-versions from Mary Sauers website. Insert the image like ClipArt,
ungroup and fill as desired.