Well, technically, you can't have a 'justified center' word because Justified means the left and right margins are the same. However, if you are trying to use tabs and center a word (as in over a column) then make sure the little arrow in the Tabs box is straight instead of 'bent.'
Pull up the tabs window and click on the little arrow that will be just above your word with the tab. Then, while the arrow is highlighted, choose Center.
Bear in mind that it will center the word under that tab; not center the word within a column so you might want to pull some guides to create your left/right 'margins' and then pull the tab to the center of that.