If you still want other users to have access to a search function, perhaps it would be satisfactory to give them permission for the google search block with your site specified in the search string.
A site specific search in google looks like this:
search term site:xoops.org
http://www.google.com/search?q=search+term+site%3Axoops.org
Just a thought for a workaround. Hope that helps.