I'd like to be able to "open up" (without unzipping) .zip files or .jar files in IntelliJ much like you can do in Eclipse by clicking the twisty. How do I do this with IntelliJ?
Jar files visible in your project structure that cannot be expanded have not yet been "added" as libraries. Right click the jar file and select Add as Library...
Also see Configuring Module Dependencies and Libraries.
And: Correct way to add lib/*.jar to an IntelliJ IDEA project