Asterisk 1.6 + A2Billing 1.8 installation and configure

We want to install Asterisk + A2Billing on a VPS server running CentOS 5. We are currently making use of a single ITSP giving us SIP to their side with multiple DIDs for incoming calls, which we will in turn assign to specific customers. We need to be able to configure our own billing/rates (different for business and after-hours) to bill customers. Monthly "line rental" should also be taken into account. Customers should be able to register to our server using SIP or IAX. We will do our own customised branding if you can show us where the images and HTML files for A2Billing are located. Basic training/instructions on where to look when something goes wrong would be essential. A basic backup of MySQL, configs and HTML files should be set up on a cron job.