Add one more item to Pat's list - Only one item is actually bound to the box. The others are hangers-on associated with the bound column, which is the value of the box if you reference it in code.
Build your ROWSOURCE query. Count the number of items returned. That has to be in the COLUMNCOUNT. The widths of the displayed items is in the COLUMNWIDTHS property in the same order as the fields are returned from the ROWSOURCE query. The BOUNDCOLUMN is usually the PK of the row's source recordset if you have one. But no matter whether you have a PK or not, you need one column to be bound as the value of the box. Oddly enough, it doesn't have to be the value you display, since it is perfectly fair game to make the column width 0 for the PK and other things that are in the hangers-on category.