The following is a tutorial on posting to your blog on MSN Spaces using the Blogjet desktop blogging application.
Create a Space on http://spaces.msn.com if you don't have one
Go to 'Edit Your Space->Settings->Email Publishing'
Turn on Email Publishing (screenshot below)
Choose a secret word (screenshot below)
Download and install the latest version of Blogjet from http://www.blogjet.com
Go to Tools->Manage Accounts
Create a new account where the user name is the name of your space (e.g. I use 'carnage4life' because the URL of my space is http://spaces.msn.com/members/carnage4life). The password is the secret word you selected when you turned on Email Publishing on your space.
On the next screen select "I already have a blog"
Specify your provider information as shown below. Host=storage.msn.com, Page=/storageservice/MetaWeblog.rpc, Port=443, Use SSL=checked (screenshot below)
Keep clicking Next until you are done
Go ahead and create, edit or delete blog posts on your space using Blogjet