Before we get started, there are some basics you should know. 
HTML & CSS are an absolute neccessity.
We will be using javascript to execute our Ajax commands. We might use some of our own functions, but we'll mostly use jQuery. It's powerful and compact. Definitely worth learning if you haven't already. 
The more PHP you know, the better! I will try to go through all the PHP in baby steps, so that we're all on the same page with PHP. 
And some knowledge of mysql will be needed.

For PHP refferences, check out these sites:
http://www.tizag.com/phpT/
http://w3schools.com/php/

MySQL refferences:
http://www.tizag.com/mysqlTutorial/
http://w3schools.com/sql/sql_select.asp

And of course the official websites are super helpful as well.
http://php.net/
http://mysql.com/