This is a good site to learn about Sun's parser and also about how to do elementary things like use SAX and DOM. It also has a nice glossary of terms. After visiting this site and learning everything on it, the content on developerlife.com (which involves real-world application of this technology) will make more sense :).

This Tutorial has 2 parts. The first part ("Overview of XML") is a high level overview of what you can do with XML in real world applications. It is not technical and illustrates the different uses for XML on the Internet. The second part ("Writing XML documents") shows how to create some simple, well-formed XML documents. It also has a neat servlet on the webpage which will parse and validate any XML that you type in the form fields.

This is not useful for parsing or generating XML documents with Java. This specification lists all the rules that apply to a well formed XML document. This document is only good for specific rules about the syntax of XML documents. 

This is very useful for parsing and generating XML documents using Java. All these interfaces are available in Java (for both the Sun and IBM parsers). The documentation for this IDL was used to create the documentation for the IBM and Sun parser's source code. This documentation is more detailed than the javadoc generated documentation for the Java interfaces in the org.w3c.dom package.

This is not useful for parsing or generating XML documents with Java. This specification lists all the rules that apply to a well formed XML document. This document is only good for specific rules about the syntax of XML documents. 

Jon Bosak, who is on the chair of the W3C XML Working Group, does a great job of describing what kinds of products and services can be made possible from the union of Java and XML.

This is David Megginson's website documenting the SAX 1.0 API. It is short and to the point. If you want to learn about SAX 1.0 I recommend reading my SAX Tutorial though :).