I have got some computers with only a JRE installed on. And to run Ant, "tools.jar" is needed witch is part of the JDK.
Instead of installing Ant and a JDK, I simply use this command (witch gives the same options than the build.xml) from the command line (or from a batch file).
java -Xmx128m -Dlog4j.configuration=config\log4j-node.properties -Djppf.config=config\jppf-node.properties -classpath lib\jppf-common-node.jar;lib\commons-logging-1.1.jar;lib\log4j-1.2.9.jar org.jppf.node.NodeLauncher
I give that just for thus who are not familiar with java arguments
Hope it can help.