Here's the minimalist Google search form that you can add to your website and lets your site user alternate search between your site or the entire Google:
Code:
<form method="get" action="http://www.google.com/search">
<input type="text" name="q" size="31"
maxlength="255" value="" />
<input type="submit" value="Google Search" />
<input type="radio" name="sitesearch" value="" />
The Web
<input type="radio" name="sitesearch"
value="yoursite url" checked /> search on this site <br />
</form>
check out Google Custom Search for another options