[movnet]

Код:

  private
    { Private declarations }
    procedure MouseWheelHandler(var Message: TMessage);override;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.MouseWheelHandler(var Message: TMessage);
var
  p:TPoint;
begin
 GetCursorPos(p);
 If WindowFromPoint(p)=DBLookupComboBox1.Handle then
 begin
  If Message.WParam<0 then
  DBLookupComboBox1.Perform(WM_VSCROLL, SB_LINEDOWN, 0)
  else
  DBLookupComboBox1.Perform(WM_VSCROLL, SB_LINEUP, 0);
 end;
end;