Are trying to "resolve" the domain name. As in are you trying to get to the website located at example.com? Do you only have 1 server in the domain now, or do you have many?

I can't access the website www.example.com from any pc in the lan, though I can from outside. I can ping the ip address of the server that hosts the website, but I can't ping www.example.com cause I can't resolve the domain name (I get "unknown host"). I've got only 1 domain controller. DNS works fine either resolving computer names internally in the lan, or resolving internet domains. But, as both domains are called example.com, when a computer in the lan tries to get to www.example.com, the pdc (which is obviously the dns server for every pc in the lan) "gets confused" because it's actually hosting a local domain itself with the same name and it never directs you to the ip address where the internet domain is actually hosted. The bottom line is - I don't know how to set up the dns server in the pdc in a way that it can resolve www.example.com right, pointing to the correct internet ip address, and still function as a domain controller.
Am I being clear? I know I don't often express myself very well. My English is not very good either. Nor my computer knowledge.