Jim Lamb has a great write up on how to build custom workflow activities for TeamBuild for TFS 2010. Given that some key activities are missing out of the box in beta two, it’s very likely you will find yourself writing a few of your own.

http://blogs.msdn.com/jimlamb/archive/2009/11/18/how-to-create-a-custom-workflow-activity-for-tfs-build-2010.aspx