LB_SETSEL

  Sets the selection state of a listbox entry.

Parameters
  wParam is 0 if the item is to be de-selected, and non-zero if the item is
   to be selected.
  LOWORD(lParam) is the index of the listbox entry to select or de-select.
   If LOWORD(lParam) is -1, then all of the entries will be selected or
   de-selected, depending on the value of wParam.