Horizontal tab - menu link

Hi, i've been fiddling with the drupal hooks for quite some time now but can't seem to get this (very simple) thing to work.

What i want to achieve is to have a horizontal tab item (Edit) with a link to the form edit page (so no content under the tab). For some reason i can't find where to hook and adjust the htab element. Can someone point me in the right direction here,

Thanks