This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
JDK 1.4+ comes with crimson parser (default implementation for JAXP 1.2 ie SAX 2 and DOM 2 APIs) so its available to you automatically. Xerces, which some people feel is better, is maintained by the Apache Software Foundation. You must download it as a JAR file and place it in your classpath (or ext directory) before you can use it. Either parser library is fine for most cases, but Xerces supports W3C XML Schema validation while Crimson doesn't.