In Server 2008, the default protocol is IPv6. It is not recommended to disable it in any way.
Default DNS, internal and LAN-wide, is therefore also IPv6. All you really need is an AAAA record for the forward lookup. But in many cases reverse lookup will have been skipped at server setup, and in such a case, it can get confusing to try to set up reverse DNS. Reverse DNS is definitely recommended, it will smoothen out the LAN in general.
It has been very difficult to find any instructions to set up reverse IPv6 DNS on Server 2008. Howsomever, here is one.