It would be a big +1 for this module to require the Vertical Tabs module, which has code to use to vertical-tabify other forms beside node forms. That way you don't have to duplicate code and encourages people to use an awesome module that is included in Drupal 7. Will post a patch later tonight.
Comments
Comment #1
greenskin commentedI look forward to your patch!
Comment #2
dave reidAfter some investigation, it's not possible to do this with Vertical Tabs because of the very specific way this form is constructed. It is possible in D7, but moot point for D6. Keep moving with your custom solution, it's the best way.