Vista - stackpanel margin animation question

Hi!
I started learning WPF today and want to create an animation for my
school homework.


I have 2 stackpanels in different margins (they are not always like
these ones. um... they are random, actually).

for example :
stack1 (0,0,0,0)
stack2 (0,0,100,0)

then I do a thickness animation :

<ThicknessAnimation Storyboard.TargetName="stack1"
Storyboard.TargetProperty="Margin" From="0,0,0,0" To="0,0,-200,0"
Duration="0:0:1" BeginTime="0:0:0.01" />
<ThicknessAnimation Storyboard.TargetName="stack2"
Storyboard.TargetProperty="Margin" From="0,0,0,0" To="0,0,-200,0"
Duration="0:0:1" BeginTime="0:0:0.02" />

then, why the final result is
stack1 (0,0,-200,0)
stack2 (0,0,-100,0)

I have put on the stack1 animation : FROM="0,0,0,0", but it doesnt
work because the animation start from 0,0,100,0 anyway.

how to move the stack1 from any coordinates into 0,0,0,0 first, before
animating it?

Thanks a lot!