Sean
Assuming your new address has an association to the contact set, I believe this will do what you want:
[Addresses.Address_Contact/Contact.Contact/Addresses.Address_Contact = '[%CurrentObject%]']
So you are traversing 'up' the association to the attached Contact and then back 'down' the association to the Addresses attached to that Contact. If you would like to exclude the Address record you are currently editing from the datagrid, you could add
[.... and id != '[%CurrentObject%]']
Hope that helps.
Mike
I am assuming your contact is the encapsulating view for the addresses datagrid, in that case, the XPath would look something like this:
[Core.Contact_Address = '[%CurrentObject%]']
Make sure to change the module name and association name to match your situation but this should allow you to retrieve all addresses belonging to a certain contact. Be aware that all objects need to be committed to the database for this to work.