MathType is quite a popular add-in for MS Office suit and is used by thousands of corporate users. It is a powerful equation editor that adds mathematical notation for word processing, web pages, desktop publishing, presentations and for TeX, LaTeX, and MathML documents.
The problem is that the current version of the add-in is not compatible with Office 2010 Beta, there is however a small fix.
To integrate MathType in Word 2010, you need to copy the following two files:
<Mathtype Installation Path>\MathPage\MathPage.wll
<Mathtype Installation Path>\MathPage\MathType Commands 6 For Word.dotm
and paste them in the following directory:
<Office Installation Path>\Office14\STARTUP\
Now restart Word 2010 and you will find the MathType tab which will replace the default Equation Editor.