From here:
To make it disappear, you need to locate the Office Assistant dialog box. You access this dialog box by Control-clicking the Office Assistant character and selecting Options from the pull-down menu. Then simply uncheck everything you don't want it to do. If you want Office Assistant back, you can still access it by choosing Microsoft Word Help from the Help menu.
I don't own or otherwise have a copy of Office for Mac, so I hope that's right.
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Bitt Faulk