I, too, agree with Dirk. This can be quite difficult.
However, I think, Writely does allow use of Blogger, MetaWeblog and MovableType APIs. It allows posting to a URL provided by the user.
Once you click on Settings inside Writely (now docs.google.com) and click on Blog Settings, you come across this part.
But, I also came across the following:
http://groups.google.com/group/How-t...4efacb154cf3ad
which says, you can't save Writely documents in place other than Google servers.
Need to think ...