WordPress Version Check provides you with an easy way of checking that you are running the most up-to-date WordPress version. The plugin checks an XML-RPC webservice every 15 minutes for update information and displays a message in the admin pages.
Note this plugin is no longer useful or supported so don’t bother installing it
See this blog post for more info: http://blog.ftwr.co.uk/archives/2009/05/26/retiring-wordpress-version-check/