Alternately, you could select the graph in Excel, go to Word, select
Edit - Paste Special - then select Picture.

A more complex method which works across different platforms quite well
(Mac and PC, as well as other programs) involves copying the graph from
Excel (Ctrl C), then paste into a PowerPoint presentation (Ctrl V).
Then simply "Save As" and select .jpg file. This will save the graph
as a jpeg and then you can go back to Word, select "Insert", "Picture",
"From File", and then navigate to the jpg of the graph. This method is
guaranteed to work, and if you e-mail the doc to someone else, they
will be able to open it without problems. I have to do this regularly
when writing papers, it's a little more work, but depending on your
audience, well worth the effort.

Good luck!
Mike