If you don't mind bouncing them out to Google and back to your site, you can add "search this site with Google" without any programming whatsoever. I added the following HTML to the template for the bottom of my pages:
<form action="http://www.google.com/search" method=GET>
<INPUT TYPE=hidden name=site value=swr>
<INPUT TYPE=hidden name=q value="site:stonehenge.com">
<INPUT TYPE=text name=as_q size=31 maxlength=256 value="">
<INPUT TYPE=submit name=btnG VALUE="Search stonehenge.com with Google"
Just replace the two occurrances of "stonehenge.com" with your
domain name, and be sure that Google is hitting your site regularly.
-- Randal L. Schwartz, Perl hacker
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