MsoBottomDock button on taskbar

A user has a button on his taskbar that reads MsoBottomDock. He has no idea when it showed up, or how it got there, and a right-click on it will not bring up any menus, and a left-click doesn’t bring up any window. Any idea what this is, and where it came from, would be greatly appreciated.
User is running a Compaq Armada E500, Win98, Office 97, on a Novell network.