best practice with intranet security and menu structure

[naijacoder naijacoder]

Here goes the scenario..
The intranet is using windows Auth integrated wih Active Directory.
Which is fine and all the appropriate Roles/Groups are set.
When a user clicks on a button on a page he/she is prompted and logs on
and
authorisation takes place
and he gets redirected to the page depending on the GROUP/ROLES they
belong
to in the active directory.
On the pages they have treeview webcontrol as a menu structure and the
Datasource is an XML file.
But the thing is each of the pages has got a different XML because they
don't want them to see the same links(menu).
And in that case its very difficult to maintain because anytime they
want to
change the MENU structure they
have to go to each XML file and change it.
What would be the best way to have one XML file with all the links and
pass
the right links(data to the Treeview menu) to the right page based on
the
seurity GROUPS/ROLES from the active directory
That means when the user logs in and based on the GROUP he belongs to
from
the active directory the right XML(Datasource) gets populated to the
Treeview Menu structure.
Any ideas or anyone done something similar?