Web form validation - Javscript/JQuery/PHP/whatever

I have a simple form on 2 html pages, each of which is based upon a Dreamweaver template (the form is the same on both templates), that need some validation adding to them (as I've been having automated bots filling the form in and this needs to be stopped). The template is in html - a PHP solution is of course possible for the template page although ideally I would not want this (as I do not want the page names to have to be .php as opposed to .html, as they are currently). This is largely due to the fact that we use a lot of Adwords traffic and I don't want to have to change all the landing page names. I understand that this can be done with JQuery (something like [login to view URL]) - it's up to you how you do it, although I would like to avoid an HTML5 solution as not all mobile devices will work with it. The form is non-complex and just has 5 simple elements. Currently, upon filling in the form, the user is sent to a [login to view URL] ([login to view URL]). This page sends the form results to email but does NO validation. So you may want to add validation to that page if you can do it that way (presumably this would enable you to add validation in PHP; I'm not sure). The form must stay the way it is now in terms of the way it looks. You are free to completely alter the form code (and put new pages in for the form info, to be sent to i required), but the form must stay the same in a design context. It's not a big site so I will clone the entire site onto a subdomain, give you FTP and let you build and test as you see fit. I know this is a quick job for those who know what they're doing, but I would like to see relevant testimonials for similar work that you have done please.