Help with RPC?

I’m trying out the beta version of NetNewsWire Pro, specifically it’s Post to Weblog feature (cool idea). It seems to want a password, though, to post to this blog, and I don’t recall there being a password here, at least not one I’ve had to enter since I first set things up.
It also gives a 404 error when it tries to post, which makes me think that it’s guess for the RPC address to hit is the source of the problem. Has anyone set up a remote client like this before who can fill me in on the details needed?
NNW Pro guessed for the RPC URL and “home” for the Blog ID, both of which smell fishy to me. Any suggestions?