Fat Abe, if you were using LaTeX (and all of those programs can export to LaTeX format ---MathCAD needs an external utility) this wouldn't be an issue. All three programs have varying abilities to natively export to MathML (believe me, _no one_ wants to write MathML out by hand).
http://www.lyx.org is a nice graphical front-end to LaTeX which you really should try.
William