Umbraco Version: 3.0.3
LiveWriter Version: 2008 [http://get.live.com/writer/overview]
Overview:
This book will walk you through the steps needed to post content to your Umbraco 3.0.3 sites using WindowsLiveWriter. If anyone has any additions, etc. to this document, please feel free to email me at bob[at]baty-barr[dot]com.
Step One: Setting up a channel
With the latest version of Umbraco, administrators are able to create users and establish content channels for the users to be able to contribute to via WindowsLiveWriter. Notice the Content Channel tab, when a new user is created. In figure 1.1 below, you can see that there are many options that can be configured.

fig1.1
First, give the channel a name, for my purposes I want to be able to post to my blog without logging in, etc. so i called my channel 'blog'. I chose my starting content node as my blog node and my starting media node as my blogImages node in media.
I also checked the box for searching children, which I believe gives you access to all the blog posts below your starting node.
finally, I selected the document type of blogPost [which is the doctype i want to contribute to] and then specified my bodyText element as the element that will be filled as the description.
As I saw pointed out recently on the forum, you should be sure that your description field is a tinyMCE text editor field to ensure an error free publishing experience.
I tried messing with the other fields, but found no joy in doing so, if others could provide some insight on this topic, that would be great.
Step Two: Configuring your template
Well, with the release of 3.0.3 of Umbraco, combined with the latest version of WindowsLiveWriter setting things up has never been easier. Here are the steps I recommend...
First, go to the template for the document type you are utilizing for content to be added by WindowsLiveWriter -- or the master template for your site -- whichever holds the HTML HEAD content.
When editing the template, locate the small question mark icon in the editor toolbar [see figure 1.2] and click it.

fig 1.2
If you scroll to the bottom of the help window you will see a code snippet and instructions for adding info to the <head></head> tag of your template that will permit WindowsLiveWriter [via the metablogAPI] to auto discover your settings. The code chunk will look something like this.
<link rel="EditURI" type="application/rsd+xml"
href="http://www.your.com/umbraco/channels/rsd.aspx" />
<link rel="wlwmanifest" type="application/wlwmanifest+xml"
href="http://www.yourdomain.com/umbraco/channels/wlwmanifest.aspx" />
Step Three: Putting it all together
So, once you have WindowsLiveWriter installed, your channel set up in your Umbraco User and the auto discover code in your template, you can set up your WindowsLiveWriter to publish to your site.