Forum OpenACS Q&A: Re: XML RPC Validator
I have quite a bit of experience with SOAP, and believe me, you do not want to go there unless you really have no choice. It's really hell.
I think a good solution for you is the Project Open REST api http://www.project-open.com/en/package-intranet-rest
PS have these forums changed recently? I see the Reply to a message link has been replaced with a Forward button. The threading is gone too, I think.