You should be able to exchnge SOAP messages with with the HTTP library as SOAP is built on the HTTP protocol, but you will have to build and parse the SOAP XML messages yourself.
However I have found that the underlying .NET HTTP code, on which the HTTP library relies, is very picky about the correct protocol. I have just written a remote monitoring app and the HTTP based server I was connecting to sends back badly formatted responses under some situations. Internet Explorer is OK with this server as it seems very tolerant of protocol errors but .NET isn't. As the server code was not accessible to fix the problem at source (
) I had to use the Network library and implement my own (trivial) version of HTTP on top of that to get it working.