Hi Tlcdan,
Its unfortunate (for us) as your environment has decided to move out of SDP. The feature of restricting requesters not to create new request is not yet included in the application. This requirement is not requested by many other customers and hence not in priority list of features. Though you are moving to a new product, I request you to visit our forums and post your suggestions (when ever possible). Good luck.
regards,
Umashankar
Product Manager, ServiceDesk Plus.