Extracting a Single Cell Value From XAML DataGrid That has Been populated with LINQ

Question

Hello Coders:
I am having a slight problem with a current project i am working on, here are some details:

.Net = version 4.0    Silverlight = version 3.0
Visual Studio 2010 RTM.   Code Behind Language XAML C#
 
The Problem:
I have created a XAML DataGrid straight out of the toolbox and i have populated the datagrid with values from a database using LINQ, when i run the silverlight project the DataGrid successfully populates iteself with the correct values (PersonID, FirstName and Address) however now that the dataGrid is successfully populating i would like to make it so when a user selects a row in the DataGrid the address value from the datagrid is displayed in a textbox. 
so far i can make it so when an row in the datagrid is selected the textbox is populated with hello world, i have done this using the MouseButtonEventArgs function, however now i want the value from the ADDRESS column for a SELECTED ROW in the DATAGRID to be placed in the TEXTBOX instead of hello world.
I am using a XAML C# code behind.
 
I am hoping that some one can provide me some C# source code to extract a COLUMN Value from a SELECTED ROW in the datagrid and assign it to a variable.
 
Thanks in advance for all your experties.
 
Regards
Tim Hiatt