For example, you can replace Xalan with SAXON for your XSLT processor:
Locate your the 'lib/ext' directory of your JDK. On the mac, this is under '/System/Library/Frameworks/JavaVM.framework/'.
Copy the saxon.jar file to that directory.
Restart Netbeans (or other Java application).
The replaces the XSLT processor for all Java applications that use that JDK or VM.