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Just wondering why, as there could be a few solutions.
Something could be achieved by setting a 301 redirect page, I'm led to believe this would be more suitable for search engines.
You could also consider using a .htaccess file to rewrite the url.
You could also use .htaccess and set up some custom XOOPS error pages, where a user could see the search option to then search for what he came looking for.
I think there was an error module available at one point on the dev.xoops site, but that sites still down at the moment.
I'm sure there maybe some other genius ways too, but that's a few that should help.