I'd start by downloading the free app called "MAMP" , which will install a set of web tools to help you manage the default Apache server that comes on your Mac.
With it, you will be able to easily start/stop your local (and private) Apache, MySQL, and PHP server.
All your sites will be stored in the 'htdocs' directory within the MAMP folder.
Then, as others have said, read books and practice, practice, practice.
My advice would be to avoid university courses on it. Why pay thousands of dollars to go through the same book you can buy on your own?
A degree is not important in this field - a portfolio is what matters. An employer will choose someone who has no degree and an outstanding portfolio over someone with a degree who's work is lackluster. In short: in this field, portfolios speak for themselves.
I'd suggest learning things in this order:
-HTML 4.0 --> easy transition to XHTML
-Then learn CSS. Your skill in CSS will make all the difference when it comes to stunning presentation.
-Graphics. Now that you know how to use CSS to the best of your abilities, practice graphics in Photoshop to give your CSS skills some real style.
-PHP. Static pages can look nice, but dynamic content is king.
-MySQL. MySQL is the icing on PHP's cake. This way you can store data in a database, retrieve it with PHP, and style it with CSS.
Avoid WYSIWYG editors! This is HUGE. Learn the proper code and learn to do it by hand. This will help you understand what is going on and give you absolute control over your site. Don't let a program code for you; it will only hold you back. Learn to type all your code by hand.
TextWrangler is an excellent (and free) editor perfect for websites and CSS. Please, if you ignore any advice, do not ignore this. I cannot stress just how important knowing how to code is. Seriously...please please please do not, ever, for any reason, use WYSIWYG editors. It is not difficult at all, and is much more helpful in the long run. It will be much harder for you to "unlearn" the terrible code generated by these foul programs than it will be for you to learn to code by hand. This is essential if you want to be good.
Sites you might want to check out, are the w3 schools (as mentioned above),
http://www.csszengarden.com (they have an excellent book), and I HIGHLY reccomend Jeffrey Zeldman's book
Designing with Web Standards.
But above all: Practice, Practice, Practice!
The more things you try, the more you will learn. We never learning anything without first failing at it, so never get discouraged. With each mistake, you learn something. The practice process is always fun to me, and if you keep positive about, I think you will learn very fast and have a blast while doing it.