I don't remember Office 2000; I may have used it, but I recently switched directly from 2003 to 2010. Still, I know there's an option in 2010 that controls this: File, Options, Advanced; then down in the Display section, "Show all windows in the Taskbar". I know 'cause I just turned it off last night; I keep changing my mind how I like it.

You'd have to figure out for yourself whether there's an analogous option in 2000; probably you can google it.