uses Registry; 
 
function StartButtonKontextEintrag(prog, prog_name: string; setzen: boolean): 
  boolean; 
var 
  Reg: TRegistry; 
  s: string; 
begin 
  result := false; 
  Reg := TRegistry.Create; 
  s := '\Directory\shell\' + stringreplace(prog_name, '&', '', []); 
  try 
    Reg.RootKey := HKEY_CLASSES_ROOT; 
    if setzen then begin 
      if Reg.OpenKey(s, True) then begin 
        Reg.writestring('', prog_name); 
        Reg.CloseKey; 
      end; 
      if Reg.OpenKey(s + '\Command', True) then begin 
        Reg.writestring('', prog); 
        result := true; 
      end else Reg.deletekey(s); 
    end else begin 
      Reg.deletekey(s); 
      result := true; 
    end; 
  finally 
    Reg.CloseKey; 
    Reg.Free; 
  end; 
end; 
 
 
// Beispielaufruf zum setzen eines Eintrags 
procedure TForm1.Button12Click(Sender: TObject); 
begin 
  if not 
    StartButtonKontextEintrag('c:\windows\calc.exe', '&Taschenrechner', true) 
    then showmessage('FEHLER'); 
end;