If so, is the department data in active directory? If not, you could import your departments from a data source, using the connector solution. After that, you could setup a resource association between the users and the departments (again this step would be easier with the data pre-populated in AD).

I'm not sure if this is what you are looking for, but the Inv_AeX_Ac_Identification table and the Inv_AeX_EU_Contact_Detail table can be used like this if all you are looking to do is ti them together from existing data:

Select Name,
[Last Logon User],
Department
from Inv_Aex_Ac_Identification i
Left Join Inv_Aex_EU_Contact_Detail cd
on i._ResourceGuid = cd._ResourceGuid

If you have the Asset Management modules intalled, another good place is to look in vUser as well.

Hope that helps.