I have MVVM master /details like this:

<Window.Resources>

<DataTemplate  DataType="{x:Type model:EveryDay}">
    <views:EveryDayView/>
</DataTemplate>

<DataTemplate  DataType="{x:Type model:EveryMonth}">
    <views:EveryMonthView/>
</DataTemplate>



</Window.Resources>



<Grid>
    <ListBox Margin="12,24,0,35" Name="schedules"
             IsSynchronizedWithCurrentItem="True"
             ItemsSource="{Binding Path=Elements}" 
             SelectedItem="{Binding Path=CurrentElement}" 
             DisplayMemberPath="Name" HorizontalAlignment="Left" Width="120"/>
    <ContentControl Margin="168,86,32,35" Name="contentControl1"
                    Content="{Binding Path=CurrentElement.Schedule}" />
    <ComboBox Height="23" Margin="188,24,51,0" Name="comboBox1" VerticalAlignment="Top" 
               IsSynchronizedWithCurrentItem="True"
               ItemsSource="{Binding  Path=Schedules}"
               SelectedItem="{Binding Path=CurrentElement.Schedule}"
               DisplayMemberPath="Name" 
               SelectedValuePath="ID"
               SelectedValue="{Binding Path=CurrentElement.Schedule.ID}"

              />
</Grid>

This Window has DataContext class:

   public class MainViewModel : INotifyPropertyChanged
{
    public MainViewModel()
    {
        _elements.Add(new Element("first", new EveryDay("First EveryDay object")));
        _elements.Add(new Element("second", new  EveryMonth("Every Month object")));
        _elements.Add(new Element("third", new EveryDay("Second EveryDay object")));

        _schedules.Add(new EveryDay());
        _schedules.Add(new EveryMonth());


    }


    private ObservableCollection<ScheduleBase> _schedules = new ObservableCollection<ScheduleBase>();
    public ObservableCollection<ScheduleBase> Schedules
    {
        get
        {
            return _schedules;
        }

        set
        {
            _schedules = value;
            this.OnPropertyChanged("Schedules");

        }
    }


    private Element _currentElement = null;
    public Element CurrentElement
    {
        get
        {
            return this._currentElement;
        }
        set
        {
            this._currentElement = value;
            this.OnPropertyChanged("CurrentElement");
        }
    }



    private ObservableCollection<Element> _elements = new ObservableCollection<Element>();
    public ObservableCollection<Element> Elements
    {
        get
        {
            return _elements;
        }

        set
        {
            _elements = value;
            this.OnPropertyChanged("Elements");

        }
    }






    #region INotifyPropertyChanged Members

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        PropertyChangedEventHandler handler = PropertyChanged;

        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    #endregion
}

One of Views:

<UserControl x:Class="Views.EveryDayView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
>
<Grid >
    <GroupBox Header="Every Day Data" Name="groupBox1" VerticalAlignment="Top">
        <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
            <TextBox  Name="textBox2" Text="{Binding Path=AnyDayData}" />
        </Grid>
    </GroupBox>
</Grid>

I have problem with SelectedItem in ComboBox.It doesn't works correctly.