A variety of sources work together to create a Web 2.0 site
Part of the power of Web 2.0 is the separation of action, style, content and collaboration.
Action on Web 2.0 pages is controlled and scripted with JavaScript. A group of small code libraries that are free, and easily downloaded to your site. Then the codes can be called into play in a variety of ways. Most control movement, fade-in, location - basically control parts of the site.
Design is controlled by Cascading Style Sheets (or CSS), and content is still HTML (or XHTML).
Here are some links in each category.