SOAP Attachment not using any toolkit

Hi,
I am a newbie in SOAP. I need to develop a client application using Visual C++ 6.0 (OS: Win 2K/XP) for sending a file attachment to the web server using SOAP. Different SOAP toolkits (e.g. Microsoft SOAP toolkit or IBM SOAP toolkit) support this and provides some objects and APIs for sending attachment  But I am not using any toolkit and using only HTTP/POST method. Using HTTP/POST method, I've been able to post some data embedded inside SOAP message. But if I need to send an attachment, how should I proceed?

W3C document (http://www.w3.org/TR/SOAP-attachments) has described some format for sending attachment using HTTP/SOAP. But posting that SOAP request to the server URL, I'm getting a SOAP fault string that some tag of the SOAP request is not closed (But I'm sure it is closed). Is it a problem of server (on which I don't have any control) or it may be some problem in specifying the content-id in SOAP request. What could be the "content id" for my case? Can it be any unique url? ...and suppose if my attached filename be myfile.txt, what I need to mention for "href" part (where I specify the attachment inside SOAP body)

Lots of question. But if any of you can guide me, it will be a great help. Otherwise if any of you can refer me any document or sample code for sending attachment using SOAP/HTTP (not using any toolkit), that will also help.

Please mark a copy of your suggestion to my e-mail nhazra03@hotmail.com
Thanks in advance.

Nilay Hazra