If i'm not mistaken, AJAX is a serverside technolagy and not a programming language. Its around using Javascript and XML, so you would need to learn one of those to use AJAX

I would carry on with PHP, Its very widly used so you can find support any where for it, and the PHP website is great place for answers and examples.

And if your looking for more of a software development language I would start off with Visual Basic as it is pretty easy to use to pick up the basics!

Matt