<p>I have 2 columns in a Grid.  When I click a button, I want the first column to animate to the left from it's current position to 0.  So, in effect, it collapses and I'm left with just viewing a single column.</p>

Shouldn't be too hard.  You'd need to create an EventTrigger that has a BeginStoryboard that targets the grid and uses a DoubleAnimation to shrink the column width.
The example here has a similar setup.
The EventTrigger would go on the button and the DoubleAnimation's
StoryBoard.Target
would point to the ColumnDefinition you wish to shrink.
Okay, so that doesn't work so well.  You can't shrink the column directly, but you CAN set the shrinking column to fill (width="*"), set the width of the Grid and the non-shrinking column, and then shrink the entire grid.  This does work.  The below example works:
```
```
<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      WindowTitle="Opacity Animation Example" 
      Background="White">
   <StackPanel Margin="20">
      <Grid Name="MyGrid" Width="200" HorizontalAlignment="Left">
         <Grid.RowDefinitions>
            <RowDefinition Height="100"/>
         </Grid.RowDefinitions>
         <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="100"/>
         </Grid.ColumnDefinitions>
         <Rectangle HorizontalAlignment="Stretch"  
                    VerticalAlignment="Stretch" 
                    Grid.Column="0" Fill="Red"/>
         <Rectangle HorizontalAlignment="Stretch"  
                    VerticalAlignment="Stretch" 
                    Grid.Column="1" Fill="Blue"/>
      </Grid>

      <Button Name="hideButton">
         <Button.Triggers>
            <EventTrigger RoutedEvent="Button.Click">
               <BeginStoryboard>
                  <Storyboard>
                     <DoubleAnimation 
                         Storyboard.TargetName="MyGrid"
                         Storyboard.TargetProperty="(Grid.Width)" 
                         From="200" To="100" 
                         Duration="0:0:2" 
                         AutoReverse="True"  /> 
                  </Storyboard>
               </BeginStoryboard>
            </EventTrigger>
         </Button.Triggers>
      </Button>
   </StackPanel>
</Page>
```
```