in reply to Dates and formvalidation

Check the docs for Data::FormValidator (ValidateRM uses D::FV profiles). You'll want to write your own constraint, it should be fairly straightforward once you decipher the docs.

To clarify the other recommendation, don't rely on client-side code, as the client can disable any such code. You can include it to avoid server work, but you'll want the code on the server just in case anyway.