Finally I was able to get posting from ecto to behave the way I wanted. You have to set up your blog to use the metaWeblogAPI and the xmpl access point is of the form "http://yourserver/weblog/xmlrpc/yourblog." A big problem was that images I uploaded would not display in the blog. It seemed that Apple's installation of blojsom would respond to xmlrpc and upload the images but Apache couldn't see the folder. Simply creating an alias in Apache didn't seem to work. Finally I created a moved the folder into the Apache server folder (/Library/WebServer/Documents) and made a symlink to it. The next trick was using Apple's new access control lists to give root and admin both read&write access so that the web server would fetch the files without incident. The only thing that threw me off for a moment was problem with Safari where it would not fetch the image file after having once got a “file not found” error. The solution was to empty the cache.
Somewhat later on I learned about JKMount which turns out to be the right way to expose internal Tomcat directories to the webserver.
So finally I have my first “official” blog post after weeks of testing Mac OS X Server 10.4 and MarsEdit and ecto, etc.
NOTE: you cannot edit the posting date from ecto (or anywhere else for the moment) making it difficult to move an entry as I have done and still keep the original time stamp. Oh well, either I figure out how to patch it or wait for Apple's blojsom to catch up.