The below steps are no longer needed since a bug in the EPiServer version used on world.episerver.com has been fixed, as mentioned in this blog post. You should now be fine following the instructions in the EPiServer World Blogging Guidelines. That also ensures that Live Writer will know all the capabilities (publishing images etc.) of your EPiServer World blog.
After recently downloading Windows Live Writer to edit this first blog post I discovered that the instructions in the EPiServer World Blogging Guidelines were a bit outdated. Part of the remedy was reading Dariusz Macina’s blog post on the subject. However, it seems some things have changed. These are the steps I followed to get Live Writer to work with my blog:
EPiServer world uses a MetaWeblog interface, for which you need the API URL. Dariusz Macina mentions the line http://world.episerver.com/util/xmlrpc/RSD.aspx?pageid=25466 in his blog post. You will need this, but it does not seem to be available in the blog page header anymore. What is available however, is the ID of your blog, namely in the tag <meta name="CommunityPageId" content="27340" /> where I assume 27340 is the ID of my blog. I substituted this into the url to get http://world.episerver.com/util/xmlrpc/RSD.aspx?pageid=27340. Browsing to this URL indicates that the ID is actually the ID of the blog.
Create a new account in Windows Live Writer (from the Tools – Accounts menu, or use the wizard which opens the first time you use the program). Choose the “Other” account type.