Background image for a page in Silverlight

 public MainPage()
        {
            InitializeComponent();
            Loaded += new RoutedEventHandler(MainPage_Loaded);
        }

        void MainPage_Loaded(object sender, RoutedEventArgs e)
        {
            ImageBrush image = new ImageBrush();
            image.ImageSource = new BitmapImage(new Uri("/PortfolioInsight;component/Images/business_ppt_background.jpg", UriKind.Relative));
        }

Hope this will help you.

Thanks.