In Word 2007, Click the funky Windows symbol in the upper left hand corner,
click on "Word Options" in the lower right hand corner of the box that
appears, click on "Proofing", click on "AutoCorrect Options", click on "Math
AutoCorrect", check the box that reads, "Use Math AutoCorrect rules outside
of math regions" and be sure the "Replace text as you type" box is checked.
Then go to your document and type " \div ". The Division symbol will appear.
It took me a few attempts to figure this out. I could not believe it does
not under the insert Symbol drop down menu.