How To Send Authorized Request

I send programatically a request to remote server:

string xml = "SomeXML Data";
string url = @"http://someserver.com";
WebRequest request = WebRequest.Create(url);
request.Method = "Post";
request.ContentType = "text/xml";
//The encoding might have to be chaged based on requirement
UTF8Encoding encoder = new UTF8Encoding();
byte[] data = encoder.GetBytes(xml); //postbody is plain string of xml
request.ContentLength = data.Length;
Stream reqStream = request.GetRequestStream();
reqStream.Write(data, 0, data.Length);
reqStream.Close();
System.Net.WebResponse response = request.GetResponse();
System.IO.StreamReader reader = new System.IO.StreamReader(response.GetResponseStream());
string str = reader.ReadToEnd();

but this code throws error:

The remote server returned an error: (401) Unauthorized.

I know user/pass to authorize when IE ask me.