对于下载时新打开一窗口下载，下载完后需要关闭的
一种：对于较小文件可以有效：
System.IO.FileInfo file = new System.IO.FileInfo("F:\\mp3\\mp3\\别哭我最爱的人.mp3");
   Response.Clear();
   Response.ClearHeaders();
   Response.Buffer = false;
   Response.Charset="GB2312";
   Response.ContentEncoding=System.Text.Encoding.UTF8;
   Response.ContentType = "application/octet-stream";
  
   Response.AddHeader("Content-Disposition", "attachment; filename="+Server.UrlEncode("别哭我最爱的人.mp3"));
   Response.AddHeader("Content-Length", file.Length.ToString());

     
   Response.WriteFile(file.FullName);
   Response.Flush();
   Response.End();
该代码可以实现输出文件并将新打开的窗体关闭。

另一种对于大文件，我们用上述代码不是较好，因为上述代码是将文件全缓存于服务器后才输出的，如果你的服务器流量大，且文件较大，不建议用以上方法。

以下我测试过，较好能解决：
public static bool ResponseFile(HttpRequest _Request,HttpResponse _Response,string _fileName,string _fullPath, long _speed)
  {
   try
   {
    FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
    BinaryReader br = new BinaryReader(myFile);
    try
    {
     _Response.AddHeader("Accept-Ranges", "bytes");
     _Response.Buffer = false;
     long fileLength = myFile.Length;
     long startBytes = 0;
    
     int pack = 10240; //10K bytes
     int sleep = (int)Math.Floor(1000 * pack / _speed) + 1;
     if (_Request.Headers["Range"] != null)
     {
      _Response.StatusCode = 206;
      string[] range = _Request.Headers["Range"].Split(new char[] {'=', '-'});
      startBytes = Convert.ToInt64(range[1]);
     }
     _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
     if (startBytes != 0)
     {
      _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength-1, fileLength));
     }
     _Response.AddHeader("Connection", "Keep-Alive");
     _Response.ContentType = "application/octet-stream";
     _Response.AddHeader("Content-Disposition","attachment;filename=" + HttpUtility.UrlEncode(_fileName,System.Text.Encoding.UTF8) );
 
     br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
     int maxCount = (int) Math.Floor((fileLength - startBytes) / pack) + 1;

     for (int i = 0; i < maxCount; i++)
     {
      if (_Response.IsClientConnected)
      {
       _Response.BinaryWrite(br.ReadBytes(pack));
       Thread.Sleep(sleep);
      }
      else
      {
       i=maxCount;
      }
     }
     _Response.Flush();
    }
    catch
    {
     return false;
    }
    finally
    {
     br.Close();
     myFile.Close();
    }
   }