Stò utilizzando questo ma purtroppo niente non mi funziona... aiuto...
Dim web As New System.Net.WebClient()
web.Headers.Add("Content-Type", "application/x-www-form-urlencoded")
Dim d As Byte() = System.Text.Encoding.ASCII.GetBytes("proposition=c onsumer&username=" & user.tostring & "password=" & pass.tostring)
Dim res As Byte() = web.UploadData("http://www.tre.it:80/selfcare/areaclienti133/4552_infoCosti_ITA_LOGGED.xsl", "POST", d)
Dim res2 As Byte() = web.DownloadData("http://www.tre.it:80/selfcare/areaclienti133/4552_infoCosti_ITA_LOGGED.xsl")
Me.RichTextBox1.Text = System.Text.Encoding.ASCII.GetString(res)