Without using the expression blend
you may just use the XAML code to achieve that
Code:
<phone:phoneapplicationpage.resources>
<storyboard x:name="ShowRectangle1">
<objectanimationusingkeyframes storyboard.targetproperty="Width" storyboard.targetname="Rectangle1">
<discreteobjectkeyframe keytime="00:00:00.03" value="25" />
<discreteobjectkeyframe keytime="00:00:00.06" value="50" />
<discreteobjectkeyframe keytime="00:00:00.09" value="75" />
<discreteobjectkeyframe keytime="00:00:00.11" value="100" />
<discreteobjectkeyframe keytime="00:00:00.15" value="125" />
<discreteobjectkeyframe keytime="00:00:00.18" value="150" />
<discreteobjectkeyframe keytime="00:00:00.21" value="175" />
<discreteobjectkeyframe keytime="00:00:00.24" value="200" />
<discreteobjectkeyframe keytime="00:00:00.28" value="250" />
<discreteobjectkeyframe keytime="00:00:00.31" value="300" />
<discreteobjectkeyframe keytime="00:00:00.34" value="350" />
<discreteobjectkeyframe keytime="00:00:00.37" value="400" />
<discreteobjectkeyframe keytime="00:00:00.40" value="450" />
<discreteobjectkeyframe keytime="00:00:00.43" value="500" />
<discreteobjectkeyframe keytime="00:00:00.46" value="550" />
<discreteobjectkeyframe keytime="00:00:00.49" value="595" />
</objectanimationusingkeyframes>
</storyboard></phone:phoneapplicationpage.resources>
in the previous code you define a storyboard called "ShowRectangle1"...
then decide what it's target object, that will be the "Rectangle1"
and the targeted property that will be "Width"
then each keytime will have a value of the width for that object(Rectangle1)
this code will be in the .xaml page that contains the rectangle
and in the code behind page you just add this to event handler let's say Page_loaded:
ShowRectangle1.Begin();
This is it