You might get an error when you install the helpdesk template "Feature ’75a0fea7-12fe-4cad-a1b2-525fa776c07e’ is not installed in this farm, and can not be added to this scope. "
The solution is to install the "ApplicationTemplatecore.wsp" which is already mentioned in the deployment instructions but you might have overlooked it just like me. But first you have to retract the solution helpdesk.wsp and ensure windows sharepoint administration service is running else the timer job will fail and you will have to use execadmsvcjobs to run the timer jobs again . You can then delete the solution and redploy after deploying Applicationtemplate core solution.
Also check if the helpdesk site is already formed by checking the content mangement and structure from the toplevel site and delete it if necessary.
Hemanth's space 