MainWindow.xaml

<Window x:Class="WPFTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition />
        </Grid.ColumnDefinitions>
        <ListBox Name="Master" Grid.Row="0" Grid.Column="0" 
                 ItemsSource="{Binding Source={StaticResource Settings}}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Path=Value[DisplayName]}"/>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
        <StackPanel Grid.Row="0" Grid.Column="1">
            <ComboBox ItemsSource="{Binding ElementName=Master, Path=SelectedValue}">
                <ComboBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Path=Value[DisplayName]}"/>
                    </DataTemplate>
                </ComboBox.ItemTemplate>
            </ComboBox>
        </StackPanel>
    </Grid>
</Window>