I'm trying to make something like this:
an html form with 5 button (each one with a differn value). if you click one of this button will be dispayed an text input (with a default value depending to the clicked button value, so the buttons call an ajax/javscript function to generate the default value) and a submit button.
I'm unable to create this type of form. have any suggestion for me ? Thx in advance.
I wouldn't use CakePHP's AJAX features, just write it yourself. Cake's features are useful in limited situations (e.g. pagination) but as soon as you need flexibility, it becomes a limiting factor. I believe the JsHelper is actually being removed in future versions.
To get this done without Cake, take a look at http://jsfiddle.net/mjxWg/8/. It's not a complete working example (e.g. there is no <form> tag), but it should show you enough to get started on your own.