If Spring is a J2EE application framework. It follows that Spring is a competitor to J2EE.
In my opinion, it's not a competitor to J2EE, but rather a complement to J2EE. Using Spring to develop your J2EE application makes things much simpler. You don't need to write nearly as much code, you get to follow best practices and J2EE
patterns, and your app will be loosely coupled. In essense, you get to quite worrying about the "architecture" of your application and start worry about the problem it's trying to solve.
I understand that SUN has been on the J2EE train for so long and Spring is a fresh birth, but how much of this functionalities does it provide outside providing one with lightweight front end and back end components?
Spring does not hide any of J2EE's APIs. You can still use any of the APIs you previously used. However, it's possible that Spring has done something to make things simpler and more configurable, so you might want to use some Spring helper classes - or at least wire up your dependencies using its IoC container.
Spring is a very non-intrusive framework that only takes a couple hours to dig in and learn about. Spring Live is designed for the Spring rookie so it should make it even simpler to learn Spring.