<sg:GcSpreadGrid Name="gcSpreadGrid1" ItemsSource="{StaticResource mySource}" 
SelectionPolicy="Range" SelectionUnit="Cell" SelectionBackground="Red" 
SelectionForeground="Blue" SelectionBackgroundUnfocused="Brown" SelectionForegroundUnfocused="Gray"
HeaderSelectionOptions="ColumnHeader|RowHeader">
<sg:GcSpreadGrid.SelectionBorder>
<sg:BorderLine Color="Black" Style="MediumDashDot"/>
</sg:GcSpreadGrid.SelectionBorder>
</sg:GcSpreadGrid>
<ComboBox ItemsSource="{Binding SelectedItems, ElementName=gcSpreadGrid1}" 
SelectedItem="{Binding SelectedItem, ElementName=gcSpreadGrid1}"
DisplayMemberPath="Name"/>