VB .Net WPF MVVM TabControl as MDI container

I'm trying to build the main window of my first MVVM style application.  The main window is fairly simple now... it contains a tabControl which I want to act as my MDI container (ala Josh Smith's article).  I've tried multiple configurations, but can't quite seem to get my first tab to show up on application launch.  Here is basically what I have so far:

Public Class Application

    Public Sub New()

        'Declare variables
        Dim vwMainWindow As New viewMainWindow

        'Set data context
        vwMainWindow.DataContext = New viewModelMainWindow

        'Show Main Window
        vwMainWindow.show()

    End Sub

End Class

Public Class Workspace

    Private _tabName As String
    Private _ViewModelName As String
    Private _ViewObject As UserControl

    Property tabName As String
        Get
            Return _tabName
        End Get
        Set(value As String)
            _tabName = value
        End Set
    End Property

    Property ViewModelName As String
        Get
            Return _ViewModelName
        End Get
        Set(value As String)
            _ViewModelName = value
        End Set
    End Property

    Property ViewObject As UserControl
        Get
            Return _ViewObject
        End Get
        Set(value As UserControl)
            _ViewObject = value
        End Set
    End Property

End Class

Imports System.Collections.ObjectModel

Public Class viewModelMainWindow

    Private _Workspaces As ObservableCollection(Of Workspace)

    Public Sub New()

        'Declare Variables
        Dim wsTimeClock As New Workspace
        Dim vwTimeClock As New viewTimeClock
        Dim collWorkspaces As New ObservableCollection(Of Workspace)

        'Set Values for wsTimeClock
        wsTimeClock.ViewModelName = "vmTimeClock"
        wsTimeClock.tabName = "Test"
        wsTimeClock.ViewObject = vwTimeClock

        'Add workspace to collection
        collWorkspaces.Add(wsTimeClock)

        'Set Public Property Workspaces to collWorkspaces
        Me.Workspaces = collWorkspaces

    End Sub

    Public Property WorkSpaces As ObservableCollection(Of Workspace)
        Get
            Return _Workspaces
        End Get
        Set(value As ObservableCollection(Of Workspace))
            value = _Workspaces
        End Set
    End Property

End Class

<Window x:Class="viewMainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
        xmlns:local="clr-namespace:WpfApplication1"
        Height="549" Width="615"><Grid RenderTransformOrigin="0.554,0.528"><Grid.RowDefinitions><RowDefinition Height="71*"/><RowDefinition Height="448*"/></Grid.RowDefinitions><Grid.ColumnDefinitions><ColumnDefinition Width="167"/><ColumnDefinition Width="440"/><ColumnDefinition Width="Auto"/></Grid.ColumnDefinitions><Menu HorizontalAlignment="Left" Height="28" VerticalAlignment="Top" Width="607" Grid.ColumnSpan="2" Margin="0,42,0,0"><MenuItem Header="File" Height="28"><MenuItem Header="Exit"/></MenuItem></Menu><Label Content="Test App" HorizontalAlignment="Left" Height="37" Margin="2,0,0,0" VerticalAlignment="Top" Width="605" FontSize="18.667" FontWeight="Bold" HorizontalContentAlignment="Center" Grid.ColumnSpan="2"/><TabControl ItemsSource="{Binding Path=DataContext.Workspaces}" Grid.Column="1" HorizontalAlignment="Left" Height="444" Margin="0,4,0,0" Grid.Row="1" VerticalAlignment="Top" Width="440"><TabControl.ItemTemplate><DataTemplate><TextBlock Text="{Binding Path=DataContext.Workspaces.tabName}"/></DataTemplate></TabControl.ItemTemplate></TabControl></Grid></Window>

I'm very new to this, so I feel like there's something simple I'm missing.  My understanding was that, by using an Observable collection, that any controls bound to the collection would automatically refresh without the need for implementing iNotifyCollectionChanged, but maybe I'm wrong.  My other thought is that I'm simply not Binding correctly in my XAML (I've probably tried 10 different variations at this point without luck).

Any help for this newbie would be greatly appreciated!!!!