WebRequest Wrq = WebRequest.Create("你要采集的地址");
                WebResponse Wrs = Wrq.GetResponse();
                Stream strm = Wrs.GetResponseStream();
                StreamReader sr = new StreamReader(strm, System.Text.Encoding.GetEncoding("UTF-8"));
                string allstrm;
                allstrm = sr.ReadToEnd();
                string strPattern = @"相关正则";
                MatchCollection Matches = Regex.Matches(allstrm, strPattern, RegexOptions.IgnoreCase | RegexOptions.Compiled);
                foreach (Match NextMatch in Matches)
                {
                    str = NextMatch.Groups["src"].Value.ToString().Trim();
                }

------解决方案--------------------
帮你写了

你看下我写的这个网址

http://topic.csdn.net/u/20081223/09/a7e18f4f-400c-420f-9bd0-7949b87bddf0.html