一个可尝试的方案，使用二进制流下载，下载地址是诸如   http://www.abc.com/down.apsx?fileid=911199   这样的连接，在   down   页面进行权限判断，比如是否登录了，当前用户的点数是否满足   911199   对应的文件的下载点数   等等

二进制下载实例代码，支持特大文件下载

string   downFilePath   =   @ "D:\openSUSE-10.2-GM-DVD-i386.iso ";   //   test   with   3.8GB,   ok   //   Server.MapPath( "~/files/somefile.iso ");
                System.IO.FileInfo   downFileInfo   =   new   System.IO.FileInfo(downFilePath);

                if   (!downFileInfo.Exists)   throw   new   Exception( "文件不存在。 ");
                const   int   CHUNK_SIZE   =   10000;   //   指定块大小
                byte[]   buffer   =   new   byte[CHUNK_SIZE];

                Response.Clear();
                //   fails   to   down   the   big   file   with   both   the   following   methods
                //   error:   System.ArgumentOutOfRangeException:   大小参数必须介于零和最大的   Int32   值之间。
                //   Response.WriteFile(downFilePath);
                //   OR
                //   Response.TransmitFile(downFilePath);   //   ASP.NET   2.0   supported
                //
                using   (System.IO.FileStream   iStream   =   System.IO.File.OpenRead(downFilePath))   {
                        long   dataLengthToRead   =   iStream.Length;
                        Response.ContentType   =   "application/octet-stream ";
                        Response.AddHeader( "Content-Disposition ",
                                                              "attachment;   filename= "   +   Server.UrlPathEncode(downFileInfo.Name));   //   对文件名进行编码
                        while   (dataLengthToRead   >   0   &&   Response.IsClientConnected)   {
                                int   lengthRead   =   iStream.Read(buffer,   0,   CHUNK_SIZE);
                                Response.OutputStream.Write(buffer,   0,   lengthRead);
                                Response.Flush();
                                dataLengthToRead   =   dataLengthToRead   -   lengthRead;
                        }                      
                }
                Response.Close();