ADODB.Stream 中文乱码问题


   public string ConvertWebControlToMHTString(string htmlString, mhtImageCollection MHTimages)
        {
            //Render WebControl to html
            string html = htmlString;            //If WebControl has images, make the html Word compatible
            if ((MHTimages != null))
            {
                fixImageLocation(ref html, ref MHTimages);
            }            CDO.MessageClass msg = new CDO.MessageClass();            ADODB.Stream stm = null;            System.IO.MemoryStream MS = null;            CDO.IBodyPart iBp = default(CDO.IBodyPart);            //Make a multipart mhtml document
            CDO.IBodyPart mainBody = default(CDO.IBodyPart);
            mainBody = msg;
            mainBody.ContentMediaType = "multipart/related";            //Make the image parts of the document
            if ((MHTimages != null))
            {                mhtImage oMhtImage1 = default(mhtImage);
                int icount = MHTimages.Count;                for (int k = 1; k <= icount; k++)
                {
                    mainBody.BodyParts.Add(k);
                }
                int j = 1;
                foreach (mhtImage oMhtImage in MHTimages)
                {
                    iBp = mainBody.BodyParts[j];
                    {
                        iBp.ContentMediaType = "image/" + oMhtImage.ImageFormat.ToString().ToLower();
                        iBp.ContentTransferEncoding = "base64";                        //ContentLocation must be the same as in the html part to make them linked
                        iBp.Fields.Append("urn:schemas:mailheader:content-location", DataTypeEnum.adBSTR, 1000000, FieldAttributeEnum.adFldUnspecified, oMhtImage.ContentLocation);
                        iBp.Fields.Update();
                        iBp.Fields.Refresh();
                    }
                    try
                    {
                        MS = new System.IO.MemoryStream();
                        oMhtImage.Image.Save(MS, oMhtImage.ImageFormat);
                        byte[] bytearray = MS.ToArray();
                        stm = iBp.GetDecodedContentStream();                        stm.Write(bytearray);
                        stm.Flush();
                    }
                    finally
                    {
                        MS.Close();
                        stm.Close();
                    }
                    j++;
                }
            }            //Make the html part of the document
            iBp = mainBody.BodyParts.Add(1);
            //mainBody.BodyParts
            iBp.ContentMediaType = "text/html";
            //iBp.ContentTransferEncoding = "quoted-printable";
            iBp.ContentTransferEncoding = "base64";
            iBp.Charset = "gb2312";
            //System.IO.Stream sstm = null;
            //sstm = iBp.GetDecodedContentStream();
            stm = iBp.GetDecodedContentStream();
            //stm.Position = 2;
            stm.Charset = "utf-8";
            stm.Type = StreamTypeEnum.adTypeText;
            //stm.Charset = "gb2312";
            // MS = new System.IO.MemoryStream();            stm.WriteText(html, ADODB.StreamWriteEnum.adWriteChar);            stm.Flush();            //stm.r
            stm = mainBody.GetStream();
            return stm.ReadText(stm.Size);
        }  stm.WriteText(html, ADODB.StreamWriteEnum.adWriteChar);改了段代码，但是假如中文有问题，原版vb的代码如下
http://www.codeproject.com/KB/aspnet/aspnethtml2mht.aspx
这里，如果html里面有中文的话，会在 return stm.ReadText(stm.Size);
这里输出乱码，据说是ADODB.Stream编码的问题，
没搞过啊，求高手帮忙解决
如：
<html><body><H1>测试功能</H1><br/><br/>测试功能</body></html>
打出的内容如下thread-index: AcqJPBcRTO514rokQpWFmrH855OB4QMIME-Version: 1.0
Content-Type: text/html;
charset"gb2312"
Content-Transfer-Encoding: 8bit
Content-Class: urn:content-classes:message
Importance: normal
Priority: normal
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579<html><body><H1>审核上报测试功能</H1><br/><br/>审核上报测试功能</body></html>
求高手帮解决