http://blogs.telerik.com/blogs/posts/09-12-10/how_to_add_a_scrollbar_to_telerik_radmenu_for_silverlight.aspx
http://www.telerik.com/community/forums/wpf/menu/scrollbar-in-radmenu.aspx
<UserControl.Resources>
<myCore:BoolInverseConverter x:Key="BoolInverseConverter"/>
<myCore:VisibilityBoolConverter x:Key="VisibilityConverter"/>
<telerik:ContainerBindingCollection x:Key="ContainerBindings">
<telerik:ContainerBinding PropertyName="IsCheckable" Binding="{Binding IsCheckable}" />
<telerik:ContainerBinding PropertyName="IsChecked" Binding="{Binding IsChecked, Mode=TwoWay}" />
<telerik:ContainerBinding PropertyName="IsSeparator" Binding="{Binding IsSeparator}" />
<telerik:ContainerBinding PropertyName="IsEnabled" Binding="{Binding IsEnabled}" />
<telerik:ContainerBinding PropertyName="StaysOpenOnClick" Binding="{Binding StaysOpenOnClick}" />
<telerik:ContainerBinding PropertyName="Icon" Binding="{Binding Image}" />
<telerik:ContainerBinding PropertyName="Command" Binding="{Binding Command}"/>
<telerik:ContainerBinding PropertyName="CommandParameter" Binding="{Binding CommandParameter}"/>
<telerik:ContainerBinding PropertyName="GroupName" Binding="{Binding GroupName}"/>
<telerik:ContainerBinding PropertyName="Value" Binding="{Binding Value}"/>
</telerik:ContainerBindingCollection>
<telerik:HierarchicalDataTemplate x:Key="MenuItemTemplate" ItemsSource="{Binding Items}"
telerik:ContainerBinding.ContainerBindings="{StaticResource ContainerBindings}">
<TextBlock Text="{Binding Text}" />
</telerik:HierarchicalDataTemplate>
<!-- Menu colors -->
<LinearGradientBrush x:Key="MenuBackground" EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FFF9F9F9" Offset="0.008"/>
<GradientStop Color="#FFE6E6E7" Offset="1"/>
</LinearGradientBrush>
<Style x:Key="MenuStyle" TargetType="telerik:RadMenu">
<Setter Property="HorizontalAlignment" Value="Stretch" />
<Setter Property="VerticalAlignment" Value="Top" />
<Setter Property="Background" Value="{StaticResource MenuBackground}"/>
<Setter Property="BorderBrush" Value="Black"/>
<Setter Property="BorderThickness" Value="1" />
</Style>
</UserControl.Resources>
<Grid Grid.Row="1" Grid.Column="0" Name="MenuAndContent">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"></ColumnDefinition>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="45"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<telerik:RadMenu Grid.Row="0" Grid.Column="0" telerik:StyleManager.Theme="Vista" Style="{StaticResource MenuStyle}" Height="30" VerticalAlignment="Top" Margin="0, 10, 0, 10"
ItemTemplate="{StaticResource MenuItemTemplate}" ItemsSource="{Binding MenuList}" />
<ScrollViewer Grid.Row="1" Grid.Column="0" x:Name="svw" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto" BorderThickness="0"
IsHitTestVisible="True" Background="White" >
<ContentControl x:Name="content" Content="{Binding CurrentView}" HorizontalAlignment="Left" VerticalAlignment="Top" Loaded="content_Loaded" Width="{Binding ElementName=svw, Path=Width}"
IsEnabled="{Binding IsReadOnly, Converter={StaticResource BoolInverseConverter}}"/>
</ScrollViewer>
</Grid>