Windows Phone 7: Highlight Selected Listbox item

I have the following XAML (simple list box with custom DataTemplate). I'm trying to figure out how to highlight the selected item (maybe background colour change). I figure I need to do something with Styles in Expression Blend but I'm not quite sure where to start... Edit: After a bit of playing around I now have this (which doesn't seem to do anything)

<phone:PhoneApplicationPage
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:Custom="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
    x:Class="SqueezeBox.StartPage"
    d:DataContext="{d:DesignData SampleData/MainViewModelSampleData.xaml}"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait"  Orientation="Portrait" 
    mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="696" 
    shell:SystemTray.IsVisible="True">
    <phone:PhoneApplicationPage.Resources>
        <Style x:Key="HighlightItemStyle" TargetType="ListBoxItem">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="ListBoxItem">
                        <StackPanel x:Name="DataTemplateStackPanel" Orientation="Horizontal">
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup x:Name="SelectionStates">
                                    <VisualStateGroup.Transitions>