463715 DNS setup and control

I have a dedicated server hosted for me by a UK isp called Fasthosts. It comes with a control panel to setup webspace and email pop boxes. I want to know if it is possible to control the DNS in a different way. I want to offer clients a template based web solution which is automated and runs off pre-defined templates. I have a CMS which currently serves pages from webspace set up manually through the fastshosts control panel What I would like to know if it is possible to have the DNS configured so that a domain is pointed to a standard index page and given a hidden ID - but the pages served using mod_rewrite so they look like standard html urls. In this way I can set up a standard set of files, a domain is given a unique id. The client can sign up to the service, enter the domain name they have created and the system allocates it a unique id. This ID is used by the DNS and also the admin section, so that when a client logs in , the username and password picks up the unique ID and this is passed through the admin section pages so that the client only sees his pages and can update them. I already have a lot of the CMS work done for this, including mod_rewrite and client login. What I am looking for is the advice and cost to set up the DNS side of the project and the initial file structure, along with a form to setup a client username, password, take the domain they input in the form, and create the unique ID in the database. I need to know if this can be done whilst also keeping the existing sites as they are setup. I would also like advice on how pop3 email boxes can be controlled by clients. All the existing work is MySql/PHP. The server is Linux running Ubuntu