Use WebRequest. From Scott Hanselman:
public static string HttpPost(string URI, string Parameters)
{
System.Net.WebRequest req = System.Net.WebRequest.Create(URI);
req.Proxy = new System.Net.WebProxy(ProxyString, true);
//Add these, as we're doing a POST
req.ContentType = "application/x-www-form-urlencoded";
req.Method = "POST";
//We need to count how many bytes we're sending.
//Post'ed Faked Forms should be name=value&
byte [] bytes = System.Text.Encoding.ASCII.GetBytes(Parameters);
req.ContentLength = bytes.Length;
System.IO.Stream os = req.GetRequestStream ();
os.Write (bytes, 0, bytes.Length); //Push it out there
os.Close ();
System.Net.WebResponse resp = req.GetResponse();
if (resp== null) return null;
System.IO.StreamReader sr =
new System.IO.StreamReader(resp.GetResponseStream());
return sr.ReadToEnd().Trim();
}