Vista - Toolbar with menu as toolbar item

Hi,
I have a Toolbar with several buttons (with images) on it.
I want that one of the buttons will open a menu, but I want that the button
that open the menu will contain an image.
I tried to add a menu as a toolbar item, but I could not attach an image to
it.

Here is my xaml:
<ToolBarPanel Margin="244,24,61.493,0" VerticalAlignment="Top" Height="56">
<ToolBar Width="348" Height="56">
<Button Height="40.138" x:Name="TBButton1">
<Image Source="Bmp1.bmp" Stretch="Fill"/>
</Button>
<Menu HorizontalAlignment="Center" VerticalAlignment="Center"
Width="45.917" Height="50.875" HorizontalContentAlignment="Center">
<MenuItem HorizontalAlignment="Center"
VerticalAlignment="Center" Width="43.917" Height="41.25"
FontStretch="Normal" FontStyle="Normal" FontWeight="Normal"
HorizontalContentAlignment="Center" Header="File">
<MenuItem Header="New"/>
<MenuItem Header="Exit"/>
</MenuItem>
</Menu>
</ToolBar>
<Image Source="Bmp2.bmp" Stretch="Fill"/>
</ToolBarPanel>

How can I achieve the desired behaviour ?

Yoav.