uses Registry; 
 
procedure TForm1.Button1Click(Sender: TObject); 
var 
  R : TRegIniFile; 
begin 
  R := TRegIniFile.Create(''); 
  with R do begin 
   RootKey := HKEY_CLASSES_ROOT; 
   WriteString('.myext','','MyExt'); 
   WriteString('MyExt','','Some description of MyExt files'); 
   WriteString('MyExt\DefaultIcon','','C:\MyApp.Exe,0'); 
   WriteString('MyExt\Shell','','This_Is_Our_Default_Action'); 
   WriteString('MyExt\Shell\First_Action','','This is our first action'); 
   WriteString('MyExt\Shell\First_Action\command','','C:\MyApp.Exe /LotsOfParamaters %1'); 
   WriteString('MyExt\Shell\This_Is_Our_Default_Action','','This is our default action'); 
   WriteString('MyExt\Shell\This_Is_Our_Default_Action\command','','C:\MyApp.Exe %1'); 
   WriteString('MyExt\Shell\Second_Action','','This is our second action'); 
   WriteString('MyExt\Shell\Second_Action\command','','C:\MyApp.Exe /TonsOfParameters %1'); 
   Free; 
  end; 
end;