Doing more advanced stuff in Wordpress would mean jumping head first into server side programming as well as DB querying too. Lots to take in, but start with looking at HTML5 + CSS3 and you will be well on your way.
I've always found w3schools to be too all encompassing. Touches on everything, goes into detail on nothing. Furious Googling and asking around on message boards such as this one is more productive.
(Edit: the "serious answer" bit is referring to my css nerd joke above, not the other answers in the thread!)
Edited by janos at 19:21:13 01-12-2012