The molecular models that I am familar with are the sphere and rod type
structures. These can easily be drawn using the Draw tools. Draw does not
create spheres, however, ovals/circles can use shading to that can
approximate a spherical appearance. Draw can create cylinders, and these can
be rotated. With some practice you can achieve 3d appearance via
foreshortening of some of the rods, as well as proportional sizing of the
spheres.
My personal drawing preference is to do drawings in powepoint and then
import the final image to word, via paste special, picture format (.png, jpg,
gif etc.).
Good luck.
--
Tom Conrad
There is a good open source vector drawing tool called inkscape:
http://www.inkscape.org
Or if you want 3D drawing you can find another good open source application
here:
http://www.blender.org/ (not for the beginner though)
There are of course some commercial vector and 3D drawing tools that are
more complete and/or user friendly. But they cost a lot.
In your case I would recommend inkscape. Draw the figure there, export to a
.png or some other file format you like and add it as a picture in word. Be
sure to keep the original file for the picture though if you need to fix it
later.
To insert a picture from a file in Word do:
Insert->Picture->From file
Then choose the file you need.
Good luck