I'm trying to get wordpress to highlight a specific item in my menu when a post (any post) is viewed. I'm thinking that adding the post to the menu item, then suppressing display of sub-menus might help, but my 'Menus configuration' page doesn't show posts as items to add to the menu.

Does anyone know why that is, or if there's a better alternative to this method?

I'm using a copy of the default twentyten theme which calls wp_nav_menu in header.php.