Meugen
I see that seems pretty straight forward, I would recommend the move to v4.0 due to the better workflow functionality which will help you drive your process. What i'm not quite sure on is is this help desk type senario purly for internal infastructure or customer infastructure, I think what I am trying to get to is will the cases, or work tickets be associated to a single customer i.e. internal or a number of customers that are external to the organisation.
The approach that I would take is to use the core account and contact entities for modeling the customer data , use service contract to manage the number of tickets (if this is just internal you can get away from using the service contracts unless departments are billable) and then customise the case entity to be you case / work ticket.
Let me know if that helps
Alistair