Try this:
>From your code:
<tr>
<td><b>Part Name:</b></td>
<td><input type="text" name="partname" size=20></td>
</tr>
change to:
<td><b>Part Name:</b></td>
 <td>
         <select name="partname">
           <option value="">Select partname </option>
           <dtml-in listPartName_sql>
              <option><dtml-var partname></option>
           </dtml-in>
        </select>
 </td>
 
ZSQL method: listPartName
===================
select * from PartNameTable