[madmai]

he conseguido esto:

Código Delphi [-]
interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,psapi,
  Dialogs;

const
  WM_XBUTTONDOWN=$020B;
  WM_XBUTTONDBLCLK=$020D;

type
  TForm1 = class(TForm)
  private
    procedure WMXButtonDown(var Message: TWMMouse); message WM_XBUTTONDOWN;
   procedure WMXButtonDblClk(var Message: TWMMouse); message WM_XBUTTONDBLCLK;
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.WMXButtonDown(var Message: TWMMouse);
begin
 showmessage('Down');
end;
procedure TForm1.WMXButtonDblClk(var Message: TWMMouse);
begin
end;

pero lo que no se ahora es diferenciar entre el xbutton1 y xbutton2 me podrias hechar un cable? gracias de antemano