Hannes Wallnöfer has provided an excellent implementation of XML-RPC for Java.
To install it, download the distribution, unzip it, and add the *.jar files to your CLASSPATH. On a Unix system, you can do this by typing:
bash$ unzip xmlrpc-java.zip
bash$ cd xmlrpc-java/lib
bash$ CLASSPATH=`pwd`/openxml-1.2.jar:`pwd`/xmlrpc.jar:$CLASSPATH