Vertical Tabs

It probably would be, but AFAIK, vertical tabs can only be applied to fieldsets with the vertical tabs module. And loading would have to work based on AJAX/AHAH, since you don't want three different lists to load all the time.

No, it is more a theming issue where you will need to at a minumum shange the style of the MENU_LOCAL_TASK menu items.

Moving this to vertical tabs will probably get this changed to a "won't fix" as that is a specific implementation to a specific problem, so unfortunately you are on your own in trying to figure it out.

Exactly. The easiest (not easy, but easiest ;) ) way for you is to *theme* the currently existing local tabs so that they look like vertical tabs. You can probably do that with a custom page-messages.tpl.php.

If you need help with that, I'd suggest that you ask in the generic support forums, mailing lists or IRC.

I'll leave this issue open, but do not expect anything in here any time soon.

Modules are free to implement vertical tabs if it's available.
http://drupal.org/handbook/modules/vertical-tabs

@Dave Reid

This isn't about a form with fieldset, it's a page with several local tasks. I don't think this can be converted to vertical tabs easily.

Ah, fair enough. I just like searching through all issues that have the phrase "vertical tabs" to see if I can help anyhow.

As noted in #4, this is a theming issue. It's been three years, so should be safe to close.