This is copied from the R5 help file and is very easy to implement (also see {CHOOSE-ONE} ,{MENUCALL} and {MENUBRANCH}):
{CHOOSE-ITEM list-range;results-range;[prompt];[title];[x];[y]} displays a dialog box that contains a list of data items; waits for the user to select one and then choose OK or Cancel; and enters the index number for the user's choice in the worksheet.
Arguments
list-range is the name or address of a single-column range that contains the items displayed in the dialog box. The items must appear one per cell in the same order that you want them to appear in the list. End the list of items in list-range with a blank cell or a cell that contains the value ERR or NA.
results-range is the name or address of a cell where 1-2-3 stores the index number of the item selected by the user. The first item in the list is numbered 0, the second item is numbered 1, and so on. If the user chooses Cancel in the dialog box, 1-2-3 leaves results-range blank.
prompt is text that appears at the top of the dialog box. Use this prompt to tell users what happens when they select an item.
title is text that appears in the title bar of the dialog box.
x is a value that specifies the horizontal position, in pixels, measured from the left side of the screen to the left side of the dialog box.
y is a value that specifies the vertical position, in pixels, measured from the top of the screen to the top of the dialog box.
If you omit x and y, the dialog box appears in the center of the screen.