dim <parametro1> as string
dim <parametro2> as string
dim <parametro3> as string
dim <parametro4> as string

<parametro1> = ""
<parametro2> = <valore parametro 2>
<parametro3> = <valore parametro 3>
<parametro4> = <valore parametro 4>

            Dim encoding As New System.Text.ASCIIEncoding
            Dim postData As String = "<nomeparametro1>=" & <parametro1> & "&<nomeparametro2>=" & <parametro2> & "&<nomeparametro3>=" & <parametro3> & "&<nomeparametro4>=" & <parametro4>
            Dim web As System.Net.WebRequest = HttpWebRequest.Create("http://xxxxx.asp?")
            web.Method = "post"
            web.UseDefaultCredentials = True
            web.ContentType = "application/x-www-form-urlencoded"

            Dim arByte As Byte() = encoding.GetBytes(postData)
            web.ContentLength = arByte.Length

            Dim newStream As IO.Stream = web.GetRequestStream
            newStream.Write(arByte, 0, arByte.Length)
            newStream.Close()

            Dim respStream As IO.Stream = web.GetResponse.GetResponseStream
            Dim reader As New IO.StreamReader(respStream)
            reader.Close()