in the templates folder... open up the defualt theme... template.htm
and remove this
<!-- Search -->
<div id="search" class="noprint">
<form action="" method="get">
<fieldset><legend>Search</legend>
<label><span class="noscreen">Find:</span>
<span id="search-input-out"><input type="text" name="" id="search-input" size="30" /></span></label>
<input type="image" src="design/search_submit.gif" id="search-submit" value="OK" />
</fieldset>
</form>
</div> <!-- /search -->