Here is a sample from the sdk.
<Canvas
xmlns="http://schemas.microsoft.com/client/2007"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
<Rectangle
x:Name="MyAnimatedRectangle"
Width="100"
Height="100"
Fill="Blue">
<Rectangle.Triggers>
<!-- Animates the rectangle's opacity. -->
<EventTrigger RoutedEvent="Rectangle.Loaded">
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
Storyboard.TargetName="MyAnimatedRectangle"
Storyboard.TargetProperty="Opacity"
From="1.0" To="0.0" Duration="0:0:5" AutoReverse="True" RepeatBehavior="Forever" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</Rectangle.Triggers>
</Rectangle>
</Canvas>
Thierry Bouquain
Ucaya
http://www.ucaya.com