If your list box row source is SQL then you can set the sorting option to Ascending for the field in question. Then requery the list box in the AfterUpdate event of whenever records have been added to the record source of the list box. Search the Access help files for the Requery method for examples.
Im not using a query for the list what i have is a listbox with company names in that on double click open a form with that companys details on and i just wanted that list sorted alphabetically to make thm quicker to find cheers
If you are hand typing the list box values into the design of the list box then I suggest that you do use a table to feed the values of your list box so that you can sort it with a SQL.