Ah, I understand now/
You want to concatenant the description from two fields in the xml file.
I know you can do this from a SQLDatasource just by specifiying the two fields in the selection criteria and joining them together with "AS"
the code-behind code to generate the items in the dropdownlist would be
DropDownList1.Items.Add(New ListItem(FirstName & " " & Lastname, CustomerId)
I will try to find some time to see if you can do the same with XML, but can't guarantee when as I'm up to my eyeballs in work.