Sounds like a good ideas but i dont know how to declare the type of
"this" (Form1) to pass it to my callback function :

struct FormReference {
   int FormRef;    // ** What is the "this" (form1) type?
   int blabla;
};

BOOL CALLBACK MyEnumWindowsProc(HWND hwnd, LPARAM lparam)
{
  //  I want to access to this->textBox1->Text in this callback
function
  lparam.FormRef->textBox1->Text+="x\n";    // ?????
  return (TRUE);
}
//...
...main()
{
  FormReference *MyFormReference;
  // *** How to define define MyFormReference.FormRef=this; ?????????
  EnumWindows((WNDENUMPROC)MyEnumWindowsProc,0);    // ** How to pass
the pointer to the structure as LPARAM for the last parameter?
}

Afters hours of trying to make the callback function as described I
restart from scratch with a working example found at  :
http://www.codeproject.com/managedcpp/cbwijw.asp   The only problem is
that this example use /oldSyntax and I manage to convert it to the new
syntax.  I'm still trying to figure out how to solve 2 errors and 1
warning.

Original /old syntax source : http://www.codeproject.com/managedcpp/cbwijw.asp

Here is the converted example :
======================
<Code>

#include "stdafx.h"
#using <mscorlib.dll>
#using <System.dll>
#using <System.Drawing.dll>
#using <System.Windows.Forms.dll>
#include <tchar.h>
#include <windows.h>

using namespace System;
using namespace System::ComponentModel;
using namespace System::Drawing;
using namespace System::Windows::Forms;

ref class CEnumWindows
{
private:
    __nogc class _CEnumWindows   //  **** Error C4980: '__nogc' : use of
this keyword requires /clr:oldSyntax ***
    {
    private:
        static  BOOL EnumWindowsProc(HWND hwnd, LPARAM)
        {
            CEnumWindows^ pew = CEnumWindows::GetClass();
            pew->m_EnumProc->Invoke(hwnd, NULL);   //*** Error C2664:
'CEnumWindows::EnumProc::Invoke' : cannot convert parameter 1 from
'HWND' to 'System::IntPtr'
            return TRUE;
        }
    public:
        void StartFinding()
        {
            EnumWindows((WNDENUMPROC)_CEnumWindows::EnumWindowsProc,NULL);
        }
    };
private:
    _CEnumWindows* m_ew;
public:
    delegate bool EnumProc(IntPtr hwnd, IntPtr lParam);
    static CEnumWindows^ GetClass()
    {
        return m_pclass;
    }
    static CEnumWindows^ m_pclass=NULL;
    CEnumWindows()
    {
        m_pclass = this;
        m_ew = new _CEnumWindows();
    }
    ~CEnumWindows()
    {
        delete m_ew;
    }
    void StartFinding()
    {
        m_ew->StartFinding();
    }
    EnumProc^ m_EnumProc;
};

public ref class NForm : public Form
{
public:
    bool EWHandler(IntPtr hwnd, IntPtr lParam)
    {
        char buff[512];
        if(GetWindowText((HWND)hwnd.ToInt32(),buff,511))
        {
            String^ s = String::Format("{0}{1}",
                hwnd.ToInt32().ToString("X8"),Convert::ToString(buff)); // ***
Warning    warning C4800: 'char *' : forcing value to bool 'true' or
'false' (performance warning) ***
            lbox->Items->Add(s);
        }
        return false;
    }
    NForm()
    {
        StartPosition = FormStartPosition::CenterScreen;
       Text = "Callbacks with IJW - Nish for CodeProject - Avoid
DllImport";
       Size = Drawing::Size(750,550);
       FormBorderStyle =
System::Windows::Forms::FormBorderStyle::FixedDialog;
        MaximizeBox = false;

        lbox = gcnew ListBox();
       lbox->Location=Point(5,5);
       lbox->Size=Drawing::Size(730,500);
        lbox->Sorted = true;

       Controls->Add(lbox);

        CEnumWindows^ p = gcnew CEnumWindows();
        p->m_EnumProc = gcnew
CEnumWindows::EnumProc(this,&NForm::EWHandler);
        p->StartFinding();

    }
    ListBox^ lbox;

};

int WinMain(HINSTANCE,HINSTANCE,LPSTR,int)
{
    Application::Run(gcnew NForm());
   return 0;
}

</Code>

Here is the ***errors*** :
==================
Error C4980: '__nogc' : use of this keyword requires /clr:oldSyntax
  -> What is the new syntax for _nogc ? cant find much details on
google...
Error C2664: 'CEnumWindows::EnumProc::Invoke' : cannot convert
parameter 1 from 'HWND' to 'System::IntPtr'
  -> ????  no idea :(
Warning    warning C4800: 'char *' : forcing value to bool 'true' or
'false' (performance warning)
  -> ????  no idea :(

If i can find solution these errors I will be ble to integrate this
"example" in my C++ form project.

Thanks again for any clues on this issues...