AJAX forms with rules?

Does anyone know of an AJAX type plug-in that I can use to make a form that has “rules”?

For example – I have a series of forms now to pre-qualify a new client. There are 4 or 5 steps in the forms process that narrow down if a client is eligible for my service. Like, they have to be from a certain state, be above a certain age, and be within a certain income level. If they do not fit all of the criteria, they’re sent to another page, or a message appears on the screen. If they do ft the criteria, the form will mail me the information.

Any suggestions or ideas for this?

Thanks,
Bill