I use a single Select Many List Box for both input and output. The user selects items in the list and saves. The next time he navigates to the page it will display what he had selected earlier.
When the page and the Listbox are displayed I would like the Listbox to show the first selected item in the list. Much like the DisplayRow property does for a Table. The list is ordered alphabetically so the items starting with 'A' are always shown when the page is displayed. If the first item selected starts with 'P' then the user does not see it and must use the scroll bar to display the selected 'P' entries.