If you don't find Microsoft Equation 3.0 under Insert | Object, then
probably Equation Editor has not been installed. To install it, Go to
Control Panel | Add/Remove Programs, select Microsoft Office, and click the
Change button. In the first page, select "Add or Remove Features." On the
next page, expand "Office Tools." Select Equation Editor and set it to "Run
from My Computer." Click the Update button, and insert the Office CD when
prompted.

Also, using Tools | Customize, you can select Equation Editor from the
commands listed for the Insert category (on the Commands tab) and drag it to
a toolbar for ease of access to EE.

--
Suzanne S. Barnhill
Microsoft MVP (Word)