AutoCorrect in Word 2008 Not Working

I am running Microsoft Office 2008 for Mac on my new MacBook Pro (10.5). I want to use AutoCorrect in order to easily work with Sanskrit diacritic markings (such as "a with macron"), which I need to use frequently.

Word Mac differs from Winword in that in Winword one can go to "Symbols," find the character desired, and program a shortcut command for that character. In Word Mac, the full font palette is not available under "symbols."

Thus it seems my solution is to program in some AutoCorrect patterns. (For example, I would like to type ;a and have ;a be automatically replaced by ā. I don't want to have to go to the character palette each time I have to insert a diacritic mark.)

So here's the situation: I go into AutoCorrect and follow all the steps, but even after I set up the "replace ___ with ____" formula, I come back to the document, and nothing happens when I enter the text-to-be-replaced.

Is this a bug/issue in Mac Word 2008? Or is there something I am just missing here?

Any other suggestions on more convenient access to Sanskrit diacritic markings?