Pop Up from ASP.NET using javascript

string strScript = "<script> ";
strScript += "var newWindow = window.showModalDialog('display.aspx', '','dialogHeight: 500px; dialogWidth: 900px; edge: Raised; center: Yes; resizable: Yes; status: Yes;');";
strScript += "</script>";
ScriptManager.RegisterStartupScript(this, this.GetType(), "PopupCP", strScript, false);