Отделяем вторичную форму от главной

class TForm2 : public TForm
{
__published:    // IDE-managed Components
private:    // User declarations
public:     // User declarations
    __fastcall TForm2(TComponent* Owner);
    void __fastcall CreateParams(TCreateParams &Params);
};

void __fastcall TForm2::CreateParams(TCreateParams &Params)
{
    TCustomForm::CreateParams(Params);
    Params.WndParent = NULL;

void __fastcall TForm2::CreateParams(TCreateParams &Params)
{
    TCustomForm::CreateParams(Params);
    Params.WndParent = NULL;
    Params.ExStyle = WS_EX_PALETTEWINDOW;
}