Form Validation class

Hello guys, at moment i'm reading "Hack Proofing your web apps" book, but it makes me scared, i have seen a class from newbienetwork.net(can't find it now), that validates user input, things like telephone number, state, country , email, and also can check if only letters or numbers are in text field, my question is this are there classes of this kind around? I would really need it. Thank You very much -- Best regards, Daniel mailto:gatop@hot.ee