Inet1.Execute strURL, "POST", "username=" + strUserName + "&passwort=" + _
  strPassword, "Content-Type: application/x-www-form-urlencoded"

 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( _
  "username=Name&passwort=Pw")
Dim res As Byte() = web.UploadData("http://url/index.php", "POST", d)
Me.RichTextBox1.Text = System.Text.Encoding.ASCII.GetString(res)