Is it possible to create form fields that appear or disappear depending on selections made in other fields?

For example: I would like to have two radio buttons labeled "Fiction" and "Non-Fiction" on my form. If the user selects "Fiction", a combo box of fiction genres will appear. If the user selects "Non-Fiction", a combo box of non-fiction genres appears instead.

Is this possible, or just wishful thinking?

Thanks,
te