JAXP 1.4 RI available in the Java.net Maven repository
The latest version of the JAXP Reference Implementation (RI), version 1.4, is currently available from the Java.net Maven repository. JAXP RI version 1.4 is part of J2SE 6.0 (a.k.a. "Mustang") and it is therefore available in the beta2 versions of the JDK and the JRE for J2SE 6.0.
The standalone JAXP RI (i.e., the version not bundled with J2SE 6.0) used to be available in multiple jars like dom.jar, xercesImpl.jar, etc. We have greatly simplified the building process for JAXP RI and are now offering just two jars: jaxp-api.jar and jaxp-ri.jar. As always, you'd need to use the endorsed mechanism to override the version of JAXP bundled with your JDK.
This is the link that you can use to browse the Maven repository at Java.net. In particular, JAXP is in the directories javax.xml.parsers and com.sun.xml.parsers. If your project depends on JAXP, and it is using Maven, you can find the corresponding POMs in those directories. We tend to update this repository on regular basis, which means that the jars that you woudl get are likely to include the latest patches.
You can find more information about JAXP and its 1.4 version in the Java.net JAXP RI page.