I was in the exactly the same situation as you. Learn PHP first because it will give you the logical framework for understanding how the web server interacts with the browser. I recommend Rasmus' book: http://www.amazon.com/Programming-PHP-Rasmus-Lerdorf/dp/1565... - it's the best text book I've ever read: he gives you exactly the right amount of detail.

Later you can pick-up Javascript. There are loads of resources for this, but learn PHP first.

I don't (and won't) use PHP, but I'd suggest starting with an O'Reilly book like http://www.oreilly.com/catalog/progphp2/