在Main Form的OnShow中，添加如下代码即可：
ShowWindow(Application.Handle,SW_HIDE)
此后，必须处理最小化消息：
private
procedure WMSysCommand(var msg: TWMSysCommand); message WM_SysCommand;
{....}
implementation
procedure TMainForm.WMSysCommand(var msg: TWMSysCommand);
begin
if msg.CmdType and $FFF0 = SC_MINIMIZE then
hide
else
inherited;
end;