Pages & Permissions

As the administrator you are able to change your user’s permission levels: http://codex.wordpress.org/user_levels.

There is also the post-levels-plugin that will show private posts after a certain permission level: http://fortes.com/projects/wordpress/postlevels

Out of curiosity, why would you want a user to change only a page? Are you sure wordpress is the correct fit for your needs? Xaraya is a good program for that sort of thing.