wpf comboboxes - setting them up as desired

I find setting up comboboxes very difficult in WPF.  I can never sure of the XAML and how to get them to look like what I want. 

First of all, I'd like the combobox to look like a combobox, with the raised appearance.  Like so:

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2nd, the combo should be bound to a lookup table.

3rd, the combo should display the property value it's bound to. 

The above example is not bound to the lookup table but is bound to the property.  It displays "CK", which is correct.

If I attempt all 3 wishes, this is the result:

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Clik here to view.

If I drop the list down, it is bound to the lookup, but then I lose the binding to the property.

Xaml:

<ComboBox x:Name="cboCaseManager"   HorizontalAlignment="Left" Margin="97.134,121,0,0" 
VerticalAlignment="Top" Width="200" 
                              DisplayMemberPath="CaseManagerItem" 
ItemsSource="{Binding Source={StaticResource CaseManagerLookup}}"
SelectedValue="{Binding Path=CaseManager}"
Grid.Column="1"/>

The coding above does bind the lookup table correctly.  What's missing is the binding to the property, which I thought I was accomplishing with the SelectedValue. 

Class:

Partial Public Class tblPatientDemographic
    ...snip..
    Public Property CaseManager As String
    ...snip...
    Public Overridable Property tlkpCaseManager As tlkpCaseManager

Is it possible to do all three?

Thanks.