I strongly urge purchasing MathType. It is made by the same folks who
originally wrote the WORD equation editor, it is much more powerful and
easier to use, and integrates equations seamlessly into WORD documents.
It also seems to be the case that anyone else's WORD will read your
document, equations and all, without installing MathType.
They are at www.mathtype.com
or info@mathtype.com
Not terribly expensive I don't think. I got mine at the Baltimore AMS
meeting where they were having a special at $75. I think the list price
was $150, but inquire. . . . I have been quite pleased with it.