<Image.Resources>
    <Storyboard x:Name="myStoryboard">
        <DoubleAnimation
        Storyboard.TargetName="myTransform"
        Storyboard.TargetProperty="Angle"
        From="0" To="360" Duration="0:0:5"
        RepeatBehavior="Forever" />
    </Storyboard>
</Image.Resources>

<phone:PhoneApplicationPage.Resources>
<Storyboard x:Name="myStoryboard">
    <DoubleAnimation
        Storyboard.TargetName="myTransformPanel" <!-- Here is a object that
                                           you'd like to move e.g. StackPanel -->
        Storyboard.TargetProperty="(UIElement.RenderTransform).(CompositeTransform.Rotation)"
        From="0" To="360" Duration="0:0:5"
        RepeatBehavior="Forever" />
    </Storyboard>
</phone:PhoneApplicationPage.Resources>

<StackPanel x:Name="myTransformPanel" >
         <StackPanel.RenderTransform>
            <CompositeTransform></CompositeTransform>
        </StackPanel.RenderTransform>
</Stackanel>