private void RegisterToolStripMenuItem_Click(object sender, EventArgs e)//点击“注册”后执行的代码
        {

        }

System.Diagnostics.Process.Start("IEXPLORE.EXE","http://www.test/test.php");

------解决方案--------------------
Response.Redirect("~/www.test/test.php");
跳转，路径自己写

------解决方案--------------------
System.Diagnostics.Process.Start("IEXPLORE.EXE","http://www.baidu.com");