controlling wizard's next and back buttons

[jm]

On the weekend I decided to experiment with the wizard element. I didn't
get very far. Creating a basic wizard was easy enough with text that the
user can click though as in the sample. Next I attempted to add a simple
radio button form where you had to select "yes" to agrees to the term
and conditions, but couldn't see how to control the activation of the
next button or flow through the wizards pages/panels. How do you stop
the user selecting next (or back) until the form is completed? And,
related, how do you control which wizard panel is displayed next?

Jeff.