I think anything inserted with the Equation Editor comes in as an Object. Meaning, it won't go in a cell--it will float above your worksheet. You could position it so that it looked like it was in a cell. Perhaps someone else knows of a way to get it into a cell--I couldn't find one.
You do have AutoCorrect Options in Excel (at least from 2000 on)--check in the Tools Menu, but I can't get it to correct anything but text. Which leaves out Objects created from the Equation Editor.
tj