where clsCert is a class to implemen interface ICertificatePolicy.
for example:

Imports System.Net

Public Class clsCert
Implements ICertificatePolicy

Public Function CheckValidationResult(ByVal srvPoint As ServicePoint, ByVal certificate As System.Security.Cryptography.X509Certificates.X509Certificate, ByVal request As WebRequest, ByVal certificateProblem As Integer) As Boolean Implements System.Net.ICertificatePolicy.CheckValidationResult
Return True
End Function
End Class

In additon, don't forget to supply NetworkCredential with the usual username and password stuff.