How to add additional tabs to user profiles
I believe you can implement hook_menu in a custom module and use MENU_LOCAL_TASK as the type, and the path needs to start with user/

function HOOK_menu() {
  $items['user/mypage'] = array(
    'title' =&gt; t('My Tab'),
    'type' =&gt; MENU_LOCAL_TASK,
    //'page callback' =&gt; 'mymodule_mypage', //mymodule_mypage should be a function that returns HTML for the content area
    //'page arguments' =&gt; array(0, 1, 2), // 0 is arg(0), 1 is arg(1) etc...
  );
  return $items;
}


For all the array elements see this page