Dynamically populating DropDownList in a datagrid

Question

In my web page, I have a datagrid with a DropDownList.

The item collection for this list is dependent on an option selected by the user elsewhere on the page.  The items for each option are stored in an xml file. 

When the user selects an option, I get the values for that option from the xml file and populate a dropdownlist.

So far so good.  But I can't work out how to bind this to the datagrid, to allow the user to select one of the items from the list.

Any help greatfully appreciated

Nenni M