I am using SIGAR in a java project with Maven and Spring. I have the Maven Dependency and Maven Repository included in my pom.xml file, as described in this lin
I believe it needs to be put into your programs library folder, alongside the "sigar.jar" file.
If you plan to run your program on other OS variants, you should also have a bunch of ".dll", ".so" and ".dylib" files in the same lib folder.
Edit: You can download sigar at the link below, it contains the lib files for all major platforms: http://sourceforge.net/projects/sigar/?source=navbar