iFrame eNewsletter Signups out of Convio Surveys

We have a website that uses an iFramed Convio survey as an enewsletter signup on our homepage.

To do this, we placed an iFrame on our homepage that portals a customized HTML form (some hidden inputs, a field, and submit button that all posts to survey ID #xxxx).

For a long time, we've always just returned a simple 'Thank you!' message via a separate 'thank you.html' page in that tiny little space where we have the single field on the front end. So, on the homepage, you type into a little field in a box, hit submit, and then you see "Thank you!" where the field was.

Recently, our MOSS website admins said that we could redirect the user to an entirely different 'thank you' page on a successful submit ... and a different 'oops, you did that wrong' page on an unsuccessful submit -- like the person enters 'duh' or 'example@' or '@example.com' into the field and submits. So, by typing into an iframed form, they would be redirected away from the homepage even though they're not necessarily interacting with the homepage (to my understanding).

Is that possible?  How would that work?  If it is, I wonder what I need to provide them from Convio.