I have used this code with a listbox and textbox where the user types in the textbox and the matching item in the listbox is highlighted. I have used it with spaces. It's not exact but with some minor changes should work with a combo box.

  PROCEDURE list1.Init
	select upper(myfield) from mytable where deleted() = .f.;
	        into array thisform.aSource order by myfield
  this.rowsource = "thisform.asource"
  this.requery()
  ENDPROC


  PROCEDURE text1.InteractiveChange
  thisform.list1.listindex = ;
    ceiling(ascan(thisform.asource,allt(upper(this.value)))/1)