If you want to use Windows Live Writer with WordPress you've to enable the remote publishing option in the WordPress Settings » Writing.
Look for the option to enable ATOM publishing and XML-RPC.
You only need the XML-RPC option…
Check the box and then save your settings.
Go back to Windows Live Writer; create a WordPress account in the Windows Live Writer application— making sure the credentials are the same as the ones used on the WordPress blog.
You should be ready to go.
Larry Henry Jr.