Hide form and show another one from a dropdown

It does not matter what way to choose, but my client has requested that, based on the choice, one form is shown or another one is shown.
I have a choice. I can either append all the fields of one table onto another ahead of time so that only one table exists instead of two - and then hide the fields based on choice - but the amount of fields to hide is pretty extensive.
Or, I can simply show one form, and then if a choice is made through a dropdown, radio or even buttons, then show another form - is that possible? If so, how?
Mike