Binding and Run Question / Problem (would this be a framework version issue?)

New to WPF (using VS2008).  I was lucky enough to get some code samples from a responder to a previous wpf question I asked.   Most of the samples worked, but I ran into a problem with the following sample;

<Window x:Class="wpfTest1.Window3"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window3" Height="300" Width="300"><Grid><Grid.ColumnDefinitions><ColumnDefinition Width="50*"/><ColumnDefinition Width="50*"/></Grid.ColumnDefinitions><Grid.RowDefinitions><RowDefinition Height="50*"/><RowDefinition Height="50*"/></Grid.RowDefinitions><TextBox Name="txtMessage" Text="Hello" 
                 Grid.ColumnSpan="2" 
                 Grid.RowSpan="2"
                 HorizontalAlignment="Center" VerticalAlignment="Center" Width="50" TextAlignment="Center" Background="#FFD4F4FF"/><TextBlock Grid.Column="1" 
                   Background="Yellow"
                   HorizontalAlignment="Center"
                   VerticalAlignment="Center"><Run Text="{Binding Text, ElementName=txtMessage}"/><Run Text=" Centered"/></TextBlock></Grid></Window>

This sample worked fine until I included the <TextBlock...>...</TextBlock> part near the botoom which contains this line

<Run Text="{Binding Text, ElementName=txtMessage}"/>

I received the following error message:

Error 2 A 'Binding' cannot be set on the 'Text' property of type 'Run'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject. C:\Code\wpfTest1\wpfTest1\Window3.xaml 22 9 wpfTest1

At this time I don't know what this piece of code was supposed to demonstrate, but I would be very grateful if someone could explain what that bit of code is supposed to demonstrate and if there is a workaround I could apply to make it go (VS2008).  If this is a Framework version issue -- how could I make is work in VS2008?

Thanks

Rich P