[cherie]

That is in common_files/customer/content.tpl. You would want to copy that to the same place in 2-columns then make the changes there. There is already code surrounding the left-bar to prevent it from appearing in the cart and checkout. I think you'd want to add a "not" around the above code so you'd end up with something like this:

{if ($main neq 'cart' or $cart_empty) and $main neq 'checkout' and not ($main eq "catalog" and $current_category.category eq "")}