Vista - Focus on application startup

Hi,

I am writing a small app which has a single text box at present.

<Window x:Class="NativeApp.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Native App" Height="70" Width="420" BorderThickness="0">
<Grid Height="40" Width="400" >
<TextBox x:Name="InputBox" Margin="0,0,0,0"
BorderThickness="0"/>
</Grid>
</Window>


How can i get the keyboard focus in the text box without the user
actually clicking on the window at startup and everytime the user
context switches to the application ?

thanks in advance