If you look at your page's SOURCE CODE, you will see that the ZC generated html for the search facility is:
HTML Code:
<div id="navMainSearch"><form name="quick_find_header" action="http://www.plantperfection.co.uk/index.php?main_page=advanced_search_result" method="get"><input type="hidden" name="main_page" value="advanced_search_result" /><input type="hidden" name="search_in_description" value="1" /><input type="text" name="keyword" size="6" maxlength="30" style="width: 150px" value="Enter plant name here..." onfocus="if (this.value == 'Enter plant name here...') this.value = '';" onblur="if (this.value == '') this.value = 'Enter plant name here...';" /> <input type="submit" value="Find your plant!" style="width: 100px" /></form></div>
Now, if you hard code this into your template instead of what you've done:
HTML Code:
<center><FORM action="http://sschurch.co.uk/search/ksearch.cgi" method="GET" NAME="search">
<div class="searchbutton">
<INPUT TYPE="text" NAME="terms"><INPUT TYPE="submit" VALUE="Find your plant!">
</div>
... you MIGHT get what you want... Try it, I'm not sure.