>> I've got 2 columns, the 2nd one contains a code (3 digits) read from the
>> table field, and the 1st column contains the description (indented). The 1st
>> column is the only one that is displayed and listed.

Add a third column containing a copy of the first column without the indenting character and set the listbox properties to something like:

BoundColumn = 3
ColumnCount = 3
ColumnWidths = 100,10,0 && First 2 values are up to you.