This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
JAR files do have some stuff that has to do with versioning. I don't know how CAB file versioning works so I can't tell you if you can do the same things with JAR files. See the JAR File Specification for more information.