Right way to add JS and CSS to node/edit and other forms
If you wish to add JS and CSS to the node edit page in particular (or any form in general), the best and the right place to do so is the hook_form_alter() and the property you should be using is #after_build.

This comment on DO tells you exactly what to do - http://drupal.org/node/1253520#comment-4881588

Hope this helps :-)