Drop Down, ComboBox bindings and interdependencies

   you can use silverlight element binding to link the selection of one combobox to another.  for example, here would be the "parent" combobox.

<telerikInput:RadComboBox
x:Name="rcbPartyEmployer"
ItemsSource="{Binding Companies}"

SelectedItem="{Binding SelectedContact.TheContactEmployer, Mode=TwoWay}"

DisplayMemberPath="PartyName" />

and here would be the "child" combobox where it's ItemsSource property is bound to the SelectedItem property of the parent.

<telerikInput:RadComboBox
x:Name="rcbPartyManager"
ItemsSource="{Binding SelectedItem.TheOrganizationContacts, ElementName=rcbPartyEmployer}"
SelectedItem="{Binding SelectedContact.ThePartyManager, Mode=TwoWay}"

DisplayMemberPath="PartyName" />

you will have to decide on how you are going to do the data retrieval to make this work.  i found it easier to include the child properties in the query for the parent ItemsSource so you don't have to deal with asyncronous data loading but YMMV.

hope this helps,
jeff