combo/list box

I'm looking for help on a macro that when you land on
a cell a combo box appears, then when you hit enter it
disappears and what you selected is in the current cell.
The problem that I have now is the combo or list box is
over the cell I need the info in so I end up with the
text over text and the only way to escape the cell is
with the mouse the keyboard (enter or tab)has no effect
when I'm in the list box.

Thanks for any help