How can I center the alignment of the contents of the header template for a datagrid Silverlight 3?

Question

I need a checkbox in the header of my datagrid, however I can't seem to align this checkbox.

This is my xaml:

<data:DataGrid 
x:Name="myDataGrid"
VerticalAlignment="Top" 
Width="300" 
Grid.Column="0" 
AutoGenerateColumns="False">
<data:DataGrid.Columns>                    
    <data:DataGridCheckBoxColumn Binding="{Binding IsNew}" Width="80">
        <data:DataGridCheckBoxColumn.HeaderStyle>
            <Style TargetType="dataprimitives:DataGridColumnHeader">
                <Setter Property="ContentTemplate">
                    <Setter.Value>
                        <DataTemplate>
                            <Border Background="Red" Width="80" HorizontalAlignment="Center">
                                <CheckBox
                                    x:Name="chkAll" 
                                    HorizontalAlignment="Center" 
                                    HorizontalContentAlignment="Center"
                                    Click="chk_Click">
                                </CheckBox>
                            </Border>
                        </DataTemplate>
                    </Setter.Value>
                </Setter>
            </Style>
        </data:DataGridCheckBoxColumn.HeaderStyle>
    </data:DataGridCheckBoxColumn>
    <data:DataGridTextColumn Header="First Name" Binding="{Binding FirstName}" Width="50" />
    <data:DataGridTextColumn Header="Last Name" Binding="{Binding LastName}" Width="100" />
</data:DataGrid.Columns>

A screenshot of my datagrid can be seen at: http://img686.imageshack.us/img686/5109/datagrid.png

I used only the border to illustrate the problem, but I also tried Grid and Stackpanel, and also checked the box directly under the DataTemplate tag, but to no avail. How can I check the center box?

Any help would be greatly appreciated.

Answer 1

, DataGridColumnHeader 12- SortIcon. Border Margin="12,0,0,0" CheckBox, .