Windows Live Writer is a tool for writing posts to your blog. It is targeted at Windows Live Spaces, but also works with other blogging services (like Blogger). It is a WYSIWYG editor (which generates better markup than Word or older versions of Frontpage), but you can also edit the HTML directly.
Rather that knowing the link to the API used for publishing, you simple provide your blog address and username/password and it discovers what service you are using (although this will take a longer time that just providing the publishing API URL). It publishes a post on your blog to detect styles that are being used (so you may need to delete the post it makes).
Overall, quite a good tool that is easy to use.