Create a list box and in the properties, instead of choosing a field name, choose <expression>. Then, in the expression dialog box, try this: =FIELD1 & ' - ' & FIELD2 then click OK. You will then have a list box that shows all of the combinations of the two field values that occur in the data separated by a hyphen (you can format that any way you like). A single click on the values shown in the list box selects the corresponding value from each of the two fields at once.
