Vista Tutorial - Setting tooltip of a control to the lastest error

I am trying to figure out how to do the equivalent of the following in c#:

<Style x:Key=�tbStyle� TargetType=�{x:Type TextBox}�>
<Style.Triggers>
<Trigger Property=�Validation.HasError� Value=�true�>
<Setter Property=�ToolTip�
Value=�{Binding RelativeSource={RelativeSource Self},
Path=(Validation.Errors)[0].ErrorContent}�/>
</Trigger>
</Style.Triggers>
</Style>

Regards