You can make an HTTP POST using any number of technologies including:

0. Winsock
1. WinInet (wrapper over Winsock)
2. WinHttp
3. MFC (wrapper over WinInet)

To send a file you need to simulate a form-url-encoded posting with an
appropriate MIME type.  Basically, you need to build of a string that
contains the necessary headers and content to simulate a form post, and then
send it using one of the technologies above.

You can learn all the details of the form encoding by looking at the
apprproaite RFCs at www.ietf.org.  Some RFC numbers that would be of
interest include:

2045, 2046, 2047, 2048, 2049, 2854

another technique is to use a network monitor ("packet sniffer") to capture
the data sent by a standard web browser (such as IE) when executing the
actual form post.  You then simply substitute your file data into the post
at the appropriate place (and set the content length correctly, of course).

-cd