<ListBox Name="aa" >
            <ListBox.ItemContainerStyle>
                <Style TargetType="{x:Type ListBoxItem}">
                    <Style.Triggers>
                        <Trigger Property="IsSelected" Value="True">
                           <Setter Property="Template">
                                <Setter.Value>
                                    <ControlTemplate>
                                        <TextBox Text="{Binding Path=...}"></TextBox>
                                    </ControlTemplate>
                               </Setter.Value>
                             </Setter>
                        </Trigger>
                    </Style.Triggers>
                </Style>
                </ListBox.ItemContainerStyle>
        </ListBox>