<Canvas x:Name="root" 
  xmlns="http://schemas.microsoft.com/client/2007"  
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Width="260" Height="70">

  <Rectangle x:Name="rect1" Canvas.Top="10" Canvas.Left="0" Width="50" Height="50" Fill="#800220">
    <Rectangle.Triggers>
      <EventTrigger  RoutedEvent="Rectangle.Loaded" >
       <BeginStoryboard>
        <Storyboard x:Name="sb_1" 
          BeginTime="0:0:2"
          RepeatBehavior="0:0:0">
          <DoubleAnimation x:Name="anim_1" 
            Storyboard.TargetName="rect1"
            Storyboard.TargetProperty="(Canvas.Left)"
            To="200" 
          />
        </Storyboard>
       </BeginStoryboard>
     </EventTrigger>
    </Rectangle.Triggers>
  </Rectangle>
</Canvas>

