A simple ajax form – plugin or just do it?

I have a standard HTML form which posts to a PHP file that then updates some fields in MailChimp through the MailChimp API.

I want to turn the html form (long) into an answer-one-at-a-time Ajaxy form which will process each question as its’ own post.

I already have the form and php submission written and working – does anyone know a solid and simple plugin that will let me segment it into several ajaxy stand alone questions (IE answer question #4, and it slides out of the way and is replaced by #5, etc)…

or should I just try to write it myself (I have never touched Ajax before… nor am I sure that’s actually what I need in the first place).