Contact form module

Hi all,
I must create a contact module, for a site, a little particular: the site propose services that are assigned to professionals chosen by the site administrator.
It would have to work this way: the customer write on a site and an email arrive to the administrator; he decides which professional assign the work to ( and send him the contact).
From that moment the professional and customer comunicates only by the site and on the site must stay the archive of the emails
that they exchange (visible to the administrator).
What I would like is that the professional and the customer comunicate only by the mail to the site, no need to use username and password: it must be the site that manages coded mailboxes that are assigned to them but they don't have to be in contact in others ways and don't have to ask anything else to the customer.
Does anyone of you know if there is a cms or script already ready or similar to this that I can modifiy?
Thank you for your suggestions

Is it something similar to a ticketing system? I remember I've seen some free php scripts around the internet.

Yes, something like that would be fine ...

If your site(s) have c-panel there is a ticket system available in Fantastico. I'll have a look and see what is called and let you know.

Ok, there is a ticket system in Fantastico (fropm C-Panel). I got you the url to the support for them too.

Short description: osTicket is a widely-used open source support ticket system. It seamlessly integrates inquiries created via email, phone and web-based forms into a simple easy-to-use multi-user web interface. Manage, organize and archive all your support requests and responses in one place while providing your customers with accountability and responsiveness they deserve.
Homepage: http://osticket.com/

Hope this helps.