We need a ticketing system integrated with an existing website. You can choose a ticket system of your choice for this with the basic functionality. You can pick from here http://codecanyon.net/search?term=ticket%20system&category=php-scripts/help-and-support-tools . We like this one : http://codecanyon.net/item/tickets/full_screen_preview/2478843
Our site already contains a `users` table with the basic fields such as username, password, email. The user should be able to access the ticket system once he is logged into our website. We use PHP sessions to maintain the logins.
Please mention which one you will be integrating along with a cost and time frame.