I wish to access and display posts/groups/tags of my one wordpress site to a different wordpress site. So how do i do that? Can someone let me know this?

Make use of Feed http://codex.wordpress.org/WordPress_Feeds You are able to parse RSS being an XML file using PHP A RSS readers http://apptools.com/phptools/xml/rss.php

For those who have setup wordpress multisite then it can be done by utilizing switch_to_blog() function.