Chris Roane's Blog: Advanced PHP Form Validation
Last year I wrote an article in how to implement basic validation for a form with PHP. I decided to re-look at this and improve what I did in that article. This time we are going to make a more advanced PHP form that is more responsive and effective. This PHP sample code has many advantages over the previous article. Not only that, but for the most part it is easier to implement with more complexed forms where you need more than basic validation.
He uses PHP5, jQuery and a helpful validation plugin than handles a lot of the heavy lifting for you in defining a validate() method with the field names and checks to perform on them. You just apply this to the form and it works like magic. Don't forget the backend though - he includes code to check for things like values being set and specific checks on a few fields.