Breadcrumb NavXT is a breadcrumb Plugin for WordPress.
The plugin can be downloaded and unzipped right into your plugin folder or you do a SVN checkout instead.
After downloading, go to the Plugins page in your administration panel, and click the Activate link in the same row as the Breadcrumb NavXT Core plugin entry. After you've activated it, you can activate the Breadcrumb NavXT Admin plugin as well. It will provide a nice User-Interface (UI) within the Wordpress Admin to let you change many of the configuration values.