If I properly understand what you're asking, you have one of two options:
- You can break this form into two distinct pages, where the user is only prompted to select a form on the first page, and once that submits, they're presented with the further options on the second page (in such a case, CGI::Application might be useful)
- Or you would have to use client-side scripting to make the page interactive.
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Systems development is like banging your head against a wall...
It's usually very painful, but if you're persistent, you'll get through it.