HTML is a much simpler language.

HTML is very easy to learn, especially for someone familiar with the Web. In addition, the Web is overflowing with resources to help with the learning as well as great references. The World Wide Web Consortium (W3C) offers a good HTML introduction as well as many more lessons. TechRepublic provides numerous downloads about HTML, including an HTML reference guide and a CSS Reference Table.

You can find reference material from SitePoint with sites devoted to HTML and CSS.

There are tons of books available about HTML. Ian Lloyd's recently released The Ultimate HTML Reference, is a great resource in a surprisingly hard bound book. It provides a thorough discussion of each HTML element, along with example code and browser compatibility information.

Another good offering is HTML Dog: The Best-Practice Guide to XHTML and CSS.