Before we go on about setting up the server, you need to understand the various client connection options, how they affect you (a LOT!) and how you can affect them (not so much).
As we said, DA is all about IPv6, but it's going to be quite a while before the Internet itself is ready for it. Virtually all the public internet is still using IPv4, and so several technologies have been developed to allow those steam-era machines to connect. Sure, your users are running spanking new copies of Windows 7 on their computers, but their home routers are still using IPv4, and their ISPs are too.
When a Windows 7 client that is configured to use DA loads, it attempts to use a technology called 6to4 to establish the IPv6 connection that it needs. 6to4 (which sounds a lot like '64' when said out loud) is a bridging mechanism, designed to encapsulate IPv6 traffic inside IPv4 traffic, thereby allowing the computer to use IPv6 on non-IPv6 networks. Once you have DA configured and enabled...