Sub-queues

Is there any way to make some sort of hierarhical dividing of queues
into sub-queues. For example if you want a [system administration] queue
and you have [unix] and [windows] subque? Does that make sense at all or
is there another idea behind that. I’m just afraid I’d end up with too
many queues…

The second one I’m tryng to do is to have a scrip that notifyes (by
mail) the new owner of a ticket when I assign ticket to someone. I’ve
been playing with:
Condition: [On Owner Change]
Action: [Notify Owner] … some template…

without success. Which owner should it notify? The former or the new one?

Thanx for your help

Jure