if your looking to take stepping stones, I would suggest XHTML first. learn how to seperate your structure (text/markup/XHTML) from presentation (CSS).

If you really want to learn and be good at what you do take your time and learn each piece of the puzzle. With XHTML if you learn propper markup and validation than you can save yourself alot of troubles down the road.

It also wouldnt hurt to have a basic understanding of what XML is.

Javascript was the first programming language i learned just because i felt it went along with XHTML/CSS using OOP and the DOM. Javascript also felt a little more compact then PHP which i think took some of the pressure off being overwhelmed with large amounts of documentation and code study. but on the other side PHP does have alot of documentation out there which is always usefull.

usefull websites i find are
www.w3schools.com
www.w3.org
hope this could help.