There are lot of use-cases where the popup should have wizard like behavior. In the VCP 2.0.1 library there was the DialogWindow component designed for such cases. But it was redesigned from the scratch because of many usage issues from customers.
The modalPanel component now is more flexible and simple for usage. But the question is in organization of wizards using the component.
The answer is inside <rich:modalPanel> and <a4j:include> components combination. The <a4j:include> component allows to perform Ajax navigation inside included page. To read more about it, explore Rich Faces Guide.
Thus, one need just put include inside the modal panel and perform navigation inside it as shown in the simple include examples.