Platform: ASP.NET Language: VB.NET

I have a project that entails posting a series of form fields to a 3rd
party SSL web server, then pulling the results into a text file. The
specifications require a "GET" command, and the content-type should be
"multipart/form-data"

I've played around with the HttpWebRequest command but cannot get it
to work under these parameters. I also cannot find a great sample
meeting these conditions.

To be clear, I don't want the user to have to post the form, but
rather I want to do it all within my code, behind the scenes.

References to detailed samples, or sample code (meeting these
specifcations) would be wonderful.