起動時、Application->Run()の前に、Application->ShowMainFormをfalseに設定します。
WINAPI _tWinMain(HINSTANCE, HINSTANCE, LPTSTR, int)
{
try
{
Application->Initialize();
Application->MainFormOnTaskBar = true;
Application->CreateForm(__classid(TForm1), &Form1);
Application->ShowMainForm = false;
Application->Run();
}