Are there any alternatives to HttpWebRequest for posting?
I think using the HttpWebRequest for the "multipart/form" will require quite
an amount of code.

I would rather like something similar to:
HttpWebPost post = new HttpWebPost("http://somehere.over.the/rainbow");
post.setEncodingType(EncodingTypes.multipart);
post.addParameter("username", "Mr Test");
post.addParameter("password", "secret");
HttpWebResponse response = post.GetResponse();

The HttpClient java library is an excellent java-version of a this kind of
library.