How to draw a vertical line in WPF

You might look for a grid splitter like this?

<Window x:Class="WpfApplication9.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition></ColumnDefinition>
            <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Button Content="Button" HorizontalAlignment="Left" Margin="10,10,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click"/>
        <Button Content="Button" HorizontalAlignment="Left" Margin="10,37,0,0" VerticalAlignment="Top" Width="75" Click="Button_Click_1"/>
        <GridSplitter Width="5" IsEnabled="False"></GridSplitter>
    </Grid>
</Window>

If IsEnabled is set to "true" you can move the grid splitter and change
the proportions of the grid.

Detailed information on grid splitter can be found here:
http://wpf.2000things.com/tag/gridsplitter/