I wont spend much time rehashing this because Chris does a great job of it in his post, but there is a Add-in for Word 2007 that does much more than just equation editing.
And you thought "spell check" was cool - now there is "math check".
It will simplify the equation, graph it, and even solve for "x" (multiple roots for polynomials).
Check out the article and the get the Add-in here.
MS Math Add-In for Word 2007 - Marquee de Sells: Chris's insight outlet