Dan Shafer and Rachel Andrew have written a css/xhtml tutorial published at sitepoint that i personally find to be very good: concise, straight to the point, easy to read, gets the beginner grasps the css and xhtml fundamentals in one article. Very respectable achievement.

So if you wish to dive into the good practices of web development, shut down dreamweaver and read on : Rock Solid CSS Layouts [CSS Tutorials]