Hi Check the following links:
http://docs.oracle.com/javase/tutorial/essential/environment/paths.html
http://docs.oracle.com/javase/7/docs/technotes/tools/windows/classpath.html
That's a java topic, not a jBPM one.
In a maven project all the resources inside the /src/main/resources/ directory will be copied to the classpath. Unless you are doing something strange you should place the file there.