update: bah, I misread

Hi. Its a good idea to read the manual, which shows this

   %labels = ('eenie'=>'your first choice',
              'meenie'=>'your second choice',
              'minie'=>'your third choice');
   %attributes = ('eenie'=>{'class'=>'class of first choice'});
   print popup_menu('menu_name',
                            ['eenie','meenie','minie'],
          'meenie',\%labels,\%attributes);
[download]

which will print

<select name="menu_name" tabindex="1">
<option class="class of first choice" value="eenie">your first choice<
+/option>
<option selected="selected" value="meenie">your second choice</option>
<option value="minie">your third choice</option>
</select>
[download]

You see %attributes are keyed by -values. The manual says

The optional fifth parameter (-attributes) is provided to assign any of the common HTML attributes to an individual menu item. It's a pointer to an associative array relating menu values to another associative array with the attribute's name as the key and the attribute's value as the value.

individual menu items are <selects>