If you delete posts in WordPress that were once indexed by Google or bookmarked by one of your visitors, if they re-visit the link they’ll get your 404 error page.  The code below simply will re-direct them to your homepage.  Just copy the code to a file and rename it to 404.php.  In my WordPress installation, i just replaced the existing 404.php file in wp-content/themes/themename/ with the code below.

<?php

//Redirect for WordPress.
//http://howifixedit.net

header("HTTP/1.1 301 Moved Permanently");
header("Location: ".get_bloginfo('url'));

exit();

?>