Administrative overlay is a slick addition to Drupal 7, with all its shiny looks and Ajaxy bells and whistles. For some though it is more like "putting flourescent lights and windows in your computer case": it may look a little cool if that kind of thing works for you, but serves no real purpose. Moreover it slows down loading of the page, reduces working area and could be distracting.
In you are one of such people, there are generally two solutions available:
1) Disable the module completely, probably together with Toolbar module, and perhaps install well known from D6, good ol' Administration Menu in its place.
2) Or, if you do not really feel like getting rid of all overlay goodness, you can just disable it for specific pages only, with all other admin paths still making a good use of it. For this you would need to implement hook_admin_paths_alter().
Say you want to be able to create new and edit existing content in the old way, without using overlay. The hook implementation then will look like this:
/**
* Implements hook_admin_paths_alter().
*/
function MYMODULE_admin_paths_alter(&$paths) {
$paths['node/*/edit'] = FALSE;
$paths['node/add'] = FALSE;
$paths['node/add/*'] = FALSE;
}
And that's it, clear your caches and from now on content creation/edit pages will open without any overlay!