[Lionel]

I was able to find something to prevent the blank searches and minimum characters. Set the var minLength to desired character length.

here is the capture section in search.tpl

{capture name=search}
<TABLE border="0" cellpadding="0" cellspacing="0">  
<FORM method="POST" action="search.php" name="productsearchform"  OnSubmit="return submitSearchFrm();">
<INPUT type="hidden" name="simple_search" value="Y">
<INPUT type="hidden" name="mode" value="search">
<INPUT type="hidden" name="posted_data[substring]" value="" id="search_substring">
<INPUT type="hidden" name="posted_data[by_title]" value="Y">
<INPUT type="hidden" name="posted_data[by_shortdescr]" value="Y">
<INPUT type="hidden" name="posted_data[by_fulldescr]" value="Y">
<TR> 
 <TD align="right" valign="middle">
{literal}
<SCRIPT language="JavaScript">
function submitSearchFrm() {
          var minLength = 3;
          var frm = document.productsearchform;
	if (frm.search_for.value == "" || frm.search_for.value.length < minLength) {
		alert ("Please enter a minimum of 3 characters");
		return false;
	}
	var search_substring = document.getElementById("search_substring");
	search_substring.value = frm.search_for.value;
	return true;
}
</SCRIPT>
{/literal}
 
  <INPUT style="border:1px inset  #C0C0C0; color:#000000; background:#F4F4F4; height:17px; width:110px;" 

type="text" name="search_for" size="20" value="{$search_prefilled.substring|escape}">

 </TD>
 <TD align="left" valign="middle"> 
 <A href="javascript: if (submitSearchFrm()) document.productsearchform.submit();void(0);">{include 

file="buttons/search_head.tpl"}</A></TD></TR><TR>
 <TD align="center" colspan="2">
{$lng.lbl_advanced_search}</TD>
</TR>
</FORM>
</TABLE>
{/capture}