If you've played with VSTS 2010 CTP, you'll know that the Agile process template has changed, not just in title, but in fields and workflow. Since VSTS 2005, the Agile process template that shipped out-of-the-box for was called MSF for Agile Development v4.x. Part of what the process was trying to is show people how the MSF methodology can be adapted to an Agile process. It worked, but if you're a purist and try to match the MSF for Agile Development process to something that mirrors the Agile Alliance, we didn't match terminologies one-to-one. In VSTS 2010, the Agile process template will be a lot more aligned in naming conventions and work flow. Actually, it will be more Scrum-like rather than Agile (and I'm not going to get into the details of how Scrum is Agile and so on).
With that said, if you've been wanting to figure out how to customize a Team System Process template to match your development process, Microsoft MVP Brian Randell has written a good article, Streamline Team Projects With Process Templates for MSDN Magazine. It covers the two process templates that ship with TFS (MSF for Agile Development and MSF for CMMI Development), states and transition workflow, field definitions, as well as talks about the Process Editor in the Power Tools to edit the templates.
If you've ever wondered what it takes to modify or create your own process template, it's a really good article.