Thank You KADYELLEBEE!
Playing with Newzcrawler, and I was completely stumped about how to get the BlogThis! menu option to work properly with my Movable Type installation. Sadly, the MT documentation details what aspects of the Bloggar API are supported, but it doesn't specify what the “endpoint” should be for an XML-RPC client.
Two minutes with Google, and I found this page, which gave me exactly what I needed.
If you can read this, then I was able to successfully post from Newzcrawler.