Take a look at this plugin:
http://mvolo.com/blogs/serverside/archive/2007/08/12/IIS-Authentication-plugin-for-the-Wordpress-PHP-blogging-engine.aspx
IIS Auth plugin for WordPress
In a nutshell, the plugin allows WordPress to recognize IIS authentication methods, allowing the user to log in with an IIS authentication method such as Windows Authentication, Basic Authentication, or the ASP.NET forms authentication.
The WordPress blog engine would then recognize the IIS user and use it for things like writing posts, leaving comments, or performing blog administration.
This is nice because it allows you to integrate the app with the rest of your website which may be using a particular IIS or ASP.NET authentication mechanism, so that users log into wordpress the same exact way they log into the rest of your application.
