outlook express style folder view?

Hi,

I'm developing an application with an "explorer" type interface.. In other words, treeview on left and listview on right..

What I would like to do is give the user an option of showing the treeview or not.. I know how this can be down in code but what I would like to do is provide an "X" button in the upper right hand corner of the listview like you see in Outlook Express's folder view on the left..

How can this be accomplished?

Thanks,

Dan