How are you initially populating the listbox?

If from a database table, then do a SQL Select query based on your entered text in the textbox, this will allow the list box only to be populated with data for each added (or deleted) keystroke.
Code:
"SELECT myDispValue FROM myTable WHERE myDispValue LIKE '" &  myText & "%'"
You must clear the listbox before each re population of the resulting recordset.