[Zope] Add Combo Box in External method page

Dear All , I want to modify the ExternalMethod dtml page which cames in zope i have to add combobox into the external method i go into the zopehome/lib/python/Products/ExternalMethod/dtml where i get the dtml page methodAdd.dtml i add combo box this dtml page is call in ExternalMethod.py how can i modifed that is it i have to create a object for the combobox . Let me no if you havingsome information. Thanks and Regards Vaibhav Pol