이렇게도 될거 같은데요.. 폼 전체에서 참조하려면..^^;

public:        // User declarations
    TSpeedButton *CurSpeedButton[1];

/////////////////////////////////////////////////////////////

void __fastcall TForm1::SpeedButton1Click(TObject *Sender)
{
*CurSpeedButton =(TSpeedButton*)Sender;
((TSpeedButton*)Sender)->Down = !((TSpeedButton*)Sender)->Down;
}
//---------------------------------------------------------------------------

void __fastcall TForm1::SpeedButton2Click(TObject *Sender)
{
*CurSpeedButton =(TSpeedButton*)Sender;
}
//---------------------------------------------------------------------------

void __fastcall TForm1::SpeedButton3Click(TObject *Sender)
{
*CurSpeedButton =(TSpeedButton*)Sender;
}
//---------------------------------------------------------------------------

void __fastcall TForm1::Button1Click(TObject *Sender)
{
   if (*CurSpeedButton == NULL) return;
   (*CurSpeedButton)->Down = false;
   if ((*CurSpeedButton)->Name == "SpeedButton1")
      SpeedButton1Click((*CurSpeedButton));
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
   SpeedButton1->AllowAllUp = true;
   SpeedButton2->AllowAllUp = true;
   SpeedButton3->AllowAllUp = true;
}
//---------------------------------------------------------------------------