Https and X509Certificate

Hello to everyone!  I need to call some page using https and i know what whis page need a client certificate to be called. So some code i using is
url = "https://mytest/requestXml.aspx?d1=" & s & "&otdel=" & otdel & "&months=" & monthsCount
Dim req As HttpWebRequest = WebRequest.Create(url)
req.Credentials = New System.Net.NetworkCredential("myname", "password")
Dim cer As Microsoft.Web.Services2.Security.X509.X509Certificate
Dim pCertInfo As MyCert.modGlobal.X509_Certificate_info
Dim certMy As Microsoft. ...