need to fix this

Hi Below is the code in which we have two div tags and when i select one option fron radio button i need to show one block and when i select other option i need to show other block of code and hide the other , but i amnot able to do that , will any one help me in this

thanks

<script language="JavaScript" type="text/javascript">
       function showHide(el_id) {
        if (document.getElementById(el_id).style.display == "none"){
            document.getElementById(el_id).style.display = "block";
            }
        else if(document.getElementById(el_id).style.display == "block"){
            document.getElementById(el_id).style.display = "none";
        }
    }
</script>
<input type="radio" name="myName" value="0" onClick="showHide('showHideDiv');">select multiple divisions
<input type="radio" name="myName" value="1" onClick="showHide('showHideDiv');" checked="true">No Multiple Selections

<div id="showHideDiv" style="display:none;">

<table>   
         <tr>
         <td><strong>Division:</strong></td>        
         <td>   
         <select  name="div_no"  multiple="true" size="5"  >
         <cfoutput query="qryDivisions">
         <option value="div_no">#div_no# -  #div_desc#</option>       
         </cfoutput>       
         </select></td></tr>
     </table>
</div>

<div id="showHideDiv" style="display:none;">

    <table>   
        <tr>
        <td><strong>Division:</strong></td>       
        <td>   
        <select  name="div_no"  multiple="true" size="5"  >
        <cfoutput query="qryDivisions">
        <option value="div_no">#div_no# - #div_desc#</option>       
        </cfoutput>       
        </select></td></tr>
    </table>
</div>