Using the Bing Search library, this plugin will intercept your standard 404 page
and return a list of urls that may help your user find the content they are
looking for. You can limit the search to just the content on your site, set a
default search in case the computed one doesn't return any results, and set a
host of other options, all designed to provide your users with quality
recomendations.
This plugin should work out-of-the-box with most themes using the included 404
template. You can also define your own to fine tune the look and feel to match
your theme.
Upload the plugin to your blog, Activate it, then enter your Bing Application
Id (
http://www.bing.com/developers/createapp.aspx).
If you want to use the plugin in your theme's 404.php, add the line:
Where you want the results to show.