Upload simple_twitter.php to the /wp-content/plugins/ directory
Activate the plugin though the `Plugins' menu in WordPress wp-admin
Configure the plugin through the `Options -> SimpleTwitter' menu in WordPress wp-admin:
3a. Add a twitter user id for the messages you want to show
3b. Specify a time in minutes, for how long the SimpleTwitter should cache the tweet
Place <?php get_twitter_msg(); ?> where you would like the message to appear