Hi Jsquared,
Assuming you're using the Word 2007 Equation Editor and not the older
Insert=>Object=>Object=>Microsoft Office Equation 3.0 editor, there is presently only one font provided with Office 2007 that
contains all of the equation characters, that is Cambria math. Others are in development by 3rd parties, such as the
unfortunately-delayed-yet-again,
http://www.stixfonts.org Fonts for MathML (it's been in work since 2005 <g>).
You can apply other fonts to the content of an equation or outside of the equation the same as other text in Word, but the other
fonts may not contain all of the glyphs needed for your expressions that are contained in Cambria Math.
Right clicking on a selection in an Equation should include a font choice to change selected text if you want to do that.
The Equation tool uses the font size from the 'Normal' style, but has an internal setting that applies direct formatting to an
equation.
When you create an equation using Alt= the Equation tool starts off by adding Cambria Math and a hidden 'Equation' property of
direct formatting that identifies it internally as an equation.
The Equation Tool resizes content (if you're using Professional display) as you build the equation and applies direct formatting to
do that on the fly, but for font size it reports while in Professional buildup display will say that it's using the Normal style
size throughout.
The 'end of the road' behavior of the Word 2007 equations tool, where you can't use an arrow or tab key to continue can occur in a
couple of scenarios. Typing regular text, or using the Enter, Shift+Enter or Ctrl+Enter keys to start a new paragraph, new line or
new page, respectively should let you continue to add content.
Do you have your attributes for equations set to center as group, display and Professional or some other setting for Math regions?
(With the cursor in an equation -
Equation Tools=>Design=>Tools and click the launcher at the bottom right of the Tools group)
===================
Two problems I have -
1 - After I type in an equation and then move out of it (by right arrowing,
for example) the tab key will not work. I have to mouse click somewhere else
in the document and then click back to the end of the equation before the tab
will work.
2 - How can I change the default font and font size for equation? >>
--
Bob Buckland ?

MS Office System Products MVP
*Courtesy is not expensive and can pay big dividends*