WordPress.org

1. Upload twitter2posts to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Set your local timezone in WordPress Settings/General before setting-up the plugin
4. Go to Plugin Settings, write your twitter username, then click to Save & Sync
5. Plugin will create special category and imports last 20 tweets (Twitter API limitation). Every new tweet will be imported automatically.

If you want to see how to setup plugin, see tutorial on YouTube: http://www.youtube.com/watch?v=vtmtAB2C3mE