Uses ShellAPI;
const   WM_MIDASICON=WM_USER+ 1 ;

FIconData: TNotifyIconData;
procedure WMMIDASIcon(var Message: TMessage); message WM_MIDASICON;

procedure AddIcon;
begin
    with FIconData do
    begin
      cbSize := SizeOf(FIconData);
      Wnd := Self.Handle;
      uID := $DEDB;
      uFlags := NIF_MESSAGE or NIF_ICON or NIF_TIP;
      hIcon := Forms.Application.Icon.Handle;
      uCallbackMessage := WM_MIDASICON;
      StrCopy(szTip, 'MyCoolProg');
    end;
    Shell_NotifyIcon(NIM_Add, @FIconData);
end;

procedure DeleteIcon;
begin
  Shell_NotifyIcon(NIM_DELETE, @FIconData);
end;

procedure WMMIDASIcon(var Message: TMessage);
begin
// чего-то тут делаем, например...
  case Message.LParam of
    WM_RBUTTONUP: begin
                    MainForm.Close;
                  end;
    WM_LBUTTONDBLCLK: begin
                        if(MainForm.Visible)then
                          begin
                            MainForm.Hide;
                          end
                        else
                          begin
                            MainForm.Show;
                            Application.BringToFront;
                          end;
                      end;
  end;
end;