this work :
#pragma once
#using <mscorlib.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>
using namespace System::Windows::Forms;
__gc public class C_SimWindowForm : public Form {
public:

C_SimWindowForm(){
MainMenu* teste = new MainMenu();

};

};
and this dosent work: (why?) :
#pragma once
#using <mscorlib.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>
__gc public class C_SimWindowForm : public System::Windows::Forms::Form {
public:

C_SimWindowForm(){
System::Windows::Forms::MainMenu::MainMenu* teste = new System::Windows::Forms::MainMenu::MainMenu();

};

};