Silverlight 4 has introduced a new support for Right to Left Flow for Arabic and Hebrew.
All UI elements derived from frameworkElement has property of FlowDirection.
Default value is LeftToRight.
For Arabic, it can be changed to RightToLeft.
For arabic, TextBox will be placed as:
<TextBox Name="textBox1" Width="300" Height="30" FlowDirection="RightToLeft"/>
Enjoy Silverlight 4.0………..