This manages to put a border around it, but the tool bar panel takes up the whole screen.....
<Border Name="ToolBarPanelBorder" BorderThickness="5" BorderBrush="Black">
<ToolBarPanel HorizontalAlignment="Stretch" Name="toolBarPanel1" VerticalAlignment="Stretch" >
<Button Height="25" >Whazzzup!</Button>
<Button Height="25" >Whazzzup!</Button>
<Button Height="25" >Whazzzup!</Button>
</ToolBarPanel>
</Border>
But try using a grid row?
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="273*" />
</Grid.RowDefinitions>
<Border Name="ToolBarPanelBorder" BorderThickness="5" BorderBrush="Black">
<ToolBarPanel Grid.Row="0" HorizontalAlignment="Stretch" Name="toolBarPanel1" VerticalAlignment="Stretch" Orientation="Horizontal" Height="27">
<Button Height="25" >Whazzzup!</Button>
<Button Height="25" >Whazzzup!</Button>
<Button Height="25" >Whazzzup!</Button>
</ToolBarPanel>
</Border>
</Grid>
Seems to work.
You can also change BG colour as well
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="273*" />
</Grid.RowDefinitions>
<Border Name="ToolBarPanelBorder" BorderThickness="5" BorderBrush="Black" Background="Aquamarine">
<ToolBarPanel Grid.Row="0" HorizontalAlignment="Stretch" Name="toolBarPanel1" VerticalAlignment="Stretch" Orientation="Horizontal" Height="27">
<Button Height="25" >Whazzzup!</Button>
<Button Height="25" >Whazzzup!</Button>
<Button Height="25" >Whazzzup!</Button>
</ToolBarPanel>
</Border>
</Grid>