It's not possible with a combo box. With list boxes, there's a MultiSelect
property that you can set to either Simple (Multiple items are selected or
deselected by clicking them with the mouse or pressing the SPACEBAR.) or
Extended (Multiple items are selected by holding down SHIFT and clicking
them with the mouse or by holding down SHIFT and pressing an arrow key to
extend the selection from the previously selected item to the current item.
You can also select items by dragging with the mouse. Holding down CTRL and
clicking an item selects or deselects that item.)
Note, though, that you cannot bind a control to a multiselect list box: it's
only intended to be used unbound. In other words, if you're hoping that
users will be able to select multiple values and store them in a single
field in your table, you're going to be sadly disappointed. That's not how
relational databases are supposed to work, so Access doesn't allow it, at
least not in current versions (it's going to in Access 2007, but that's a
discussion for another day)
Instead, you need two tables: one to hold the main data, and one to hold the
additional data (what you want multi-selected).
