How to connect 2 Dynamic Objects ?

Hi together,
(sorry for my bad english)

i've looking for an CMS an found Xaraya and must say great job Xaraya-Team.
(is it a beta ? no, youre just kidding :o) )

i am playing around with Xaraya the last few days - puuh it's a hard play
:-) -
but i am willing to learn.

Now my question :
i saw here the Howto from eolica to add an publiction type "contact".
(03/06/03)
i followed the howto , create the "user-display-[publication].xd" and the
"user-summary-[publication].xd".
it works great, then i create another pub-type "Countries" to store
Information of Countries.

How can i connect the Contact with the Contries Object , so that i can use
an DropDown-Box in the
ContactForm to choose an Country?
i have put a DropDownBox with an DataSource of
"xar_dynamic_data.xar_dd_value" within the ContactObject.
the DropDownBox is shown , but not filled with Data (countries).
it's clear, the dropdownbox does not know where to get the data.
my problem is , how to the tell the DropDownBox to get the Data from the
CountriesObject.

Is it possible ?

thx for hints

Have a nice we
xaradabadooo
 Hannes