The first screencast is a simple "Hello Workflow" example that gives you a tour of the Windows Workflow Foundation designer and Visual Studio 2005 extensions while showing the core technology concepts. The second is a demo of the Ordering State Machine workflow application that we have published on the WindowsWorkflow.net site
here. This demo shows the benefits of a state machine workflow and shows how a workflow can be dynamically changed/updated at runtime. Pravin Indurkar and I built this demo a few months ago and we've found that it's a great way to visually show the concepts of a state machine workflow in WWF. Both screencasts are only 10 minutes long.
Please let me know if these screencasts are helpful and what additional ones you would like to see.