Which Word version are you using? I am not sure about version prior to
2002(XP), but 2002 has a diagramming utility that includes Venn
diagrams.
The command button is on the Insert menu by default.
If you don't and if it isn't available in previous versions you can
create
reasonably good Venn diagrams by using the drawing tools. I assume by
your
question that you have draw two circle of similar size and place one
over
the other. If this assumption is accurate, all that is left to do is
add
color. Apply a light color (e.g., yellow to the back circle) then apply
a
dark color (e.g., black or gray to the top circle). To bring the border
of
the back circle through and see a coloring effect in the overlapping
area,
all you need to do is apply a transparency effect to the top circle. Of
course you can experiment with color combinations to find an effect you
like.
AFAIK there is no easy (maybe no way at all) to apply a direct third
color
to the intersecting area.