How to space items evenly in a horizontal Silverlight Listbox

In Silverlight, I have a Vertical ListBox that has a Horizontal ListBox for each item. I want the items in the HorizontalListbox to space evenly across the width of the parent (Vertical) ListBox. How can I do this?

   <ListBox x:Name="MachineListBox" Background="Green">
        <ListBox.ItemTemplate>
            <DataTemplate>
            <ListBox ItemsSource="{Binding CoilList}" Background="Red" HorizontalAlignment="Stretch">
                    <ListBox.ItemsPanel>
                        <ItemsPanelTemplate>
                        <StackPanel 
                            HorizontalAlignment="Stretch"  />
                    </ItemsPanelTemplate                                >
                            </ListBox.ItemsPanel>

                    <ListBox.ItemTemplate >
                       <DataTemplate>
                                <TextBlock
                                    Text="{Binding Coil}"
                                     HorizontalAlignment="Stretch"/>
                        </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
        </DataTemplate>
            </ListBox.ItemTemplate>
    </ListBox>

From stackoverflow

• I'll take the liberty of suggesting you use a custom control of my own invention. It's called a ProportionalPanel and it does just what you need - spaces items evenly. You could use it for the ItemsPanel in the inner ListBox instead of the StackPanel. I also provide the source code, so you can tweak the logic any way you like. The relevant post on my blog is here.

  Peter : Perfect. Thanks.

• I think the proportional sizing operator will do what you're looking for. Haven't tried it but it sounds like an option. Width="*" and Margin="2*".