I downloaded this vi and tried it, it works really nice. However I it requires that you select an item from the list box before you move on to another cell. If you move on to another cell before selecting a item from the list box (which you can do) the code gets out of sync with the table.
So is there a way to require the user to select a value from the list box before they are allowed to select another cell?
There are likely many ways to get around what you want. One thing you could try is read which row the mouse is over by using the Point to Row invoke node on the listbox, and then set the value of the listbox before attempting to populate the drop down.
I haven't looked at the VI posted earlier in this thread, but see if this http://forums.ni.com/t5/LabVIEW/array-of-cluster/m-p/1822451#M625032 does what you want. It uses a ring or enumeration positioned over a cell of a table to make it appear that the drop-down is part of the table.