Show/hide Popup in Blend 4 using fade In-Out

Hi all,
I am designer i am using blend 4 & I am newbie to silverlight,
I have a popup controll here is its xaml code
<Button x:Name=“ShowPopupButton”
FontFamily=“Comic Sans MS”
FontSize=“24”
Content=“Hover On Me!” Margin=“127,0,82,39” MouseEnter=“ShowPopup” Height=“40” VerticalAlignment=“Bottom” MouseLeave=“HidePopup”/>
<Popup x:Name=“MyPopup” >
<Grid Height=“234” Width=“383” Margin=“140,100,0,0”>
<Rectangle Height=“190” Margin=“4,22,19,20” Stroke=“White” RadiusY=“10” RadiusX=“10”>
<Rectangle.Effect>
<DropShadowEffect BlurRadius=“50” Opacity=“0.69” Direction=“300” ShadowDepth=“1” Color="#FF898888"/>
</Rectangle.Effect>
<Rectangle.Fill>
<LinearGradientBrush EndPoint=“0.5,1” StartPoint=“0.5,0”>
<GradientStop Color="#FFE8F6FD" Offset=“0”/>
<GradientStop Color="#FFC5E8FA" Offset=“1”/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
<TextBlock x:Name=“PopUpText”
Text=“Name:”
FontFamily=“Arial Unicode MS” FontSize=“14.667”
Foreground="#FF101010" Margin=“18,30,0,0” Height=“23” VerticalAlignment=“Top” HorizontalAlignment=“Left” Width=“94”/>
</Grid>
</Popup>

I want to show this popup fade in and fade out. I applied to a button mouseenter to show and mouseleave to hide here is xaml.cs

private void ShowPopup(object sender, System.Windows.RoutedEventArgs e)
{
MyPopup.IsOpen = true;// TODO: Add event handler implementation here.
}
private void HidePopup(object sender, System.Windows.Input.MouseEventArgs e)
{
MyPopup.IsOpen = false;// TODO: Add event handler implementation here.
}

now what i want is fade in fade out effect when i Hover/Out

can please help on this how to do control.