I assume u want to display the listbox while you are editing the grid correct? Define the edittemplate with the dropdown and the lookupid and eventually rowid and for the dropdown control, set datasource to a function that retrieves the data , for example DataSource='<%#GetmyData(myiD)%>

You can access the props of the listbox either at runtime by getting a reference to the control (e.Item.FindControl(listobxid)) or at design time , if you choose to edit the template.