Just override ItemContainerStyle:
<ListBox ItemsSource="...">
<ListBox.ItemContainerStyle>
<Style TargetType="{x:Type ListBoxItem}">
<Setter Property="IsSelected" Value="{Binding Selected}"/>
</Style>
</ListBox.ItemContainerStyle>
</ListBox>
Oh, by the way, I think you'd like this wonderful articles from dr.WPF: ItemsControl: A to Z.
Hope this helps.
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