>Something like:
>

><ScrollViewer HorizontalScrollBarVisibilitty="Auto" VerticalScrollBarVisibility="Auto">
>    <TabControl>
>        <TabItem>
>            <Grid>
>                <Grid.ColumnDefinitions>
>                    <ColumnDefinition Width="300"/>
>                    <ColumnDefinition/>
>                </Grid.ColumnDefinitions>
>                <StackPanel>
>                        <!-- Main Content, allow horizontal scrolling, don´t allow vertical scrolling-->
>                </Stackpanel>
>                <StackPanel Grid.Column="1">  // Allow Vertical Scrolling
>                     <Expander>
>                            <!-- Description 1 -->
>                     </Expander>                     
>                     <Expander>
>                            <!-- Description 2 -->
>                     </Expander>                     
>                     <Expander>
>                            <!-- Description 3 -->
>                     </Expander>                     
>                </StackPanel>
>            </Grid>
>        </TabItem>
>        ...
>    </TabControl>
></ScrollViewer>
>

Why can't you use two ScrollViewers' (one for each column) as I suggested ?