Theming the node edit forms  to open them within Lightbox
If installing one or 2 additional module is an option then you can check Popups API (Ajax Dialogs). When I last checked, the module had functionality of opening forms in popups, which you can theme. I also feel that, in the way Drupal form API works, there is more to done then just adding classes and JavaScript to make Drupal forms work in Lightbox.