In that case, you want to replace the aforementioned <input> element in form.tmpl with a <select> element with an HTML::Template loop inside it:

<select name="dept">
<TMPL_LOOP NAME="DEPT_LOOP">
<option value="<TMPL_VAR NAME="DEPT">"><TMPL_VAR NAME="DEPT">
</TMPL_LOOP>
</select>
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Then, from within your script, you want to select all possible departments from your database, and populate that list using the loop name (DEPT_LOOP in the example). For more info on how to do that, see the HTML::Template docs.