Yes, the latest version of Eclipse is called "Ganymede." Have you tried running anything from the command line? Go through the "Getting Started" Section of the Java Tutorials. Do you get any problems? Do you get any error messages? The "common problems" link tells you about them, and what to do. There is a link to how to set up your PATH in the common problems page.
I suspect this is a PATH problem; when you install NetBeans you set up a JAVA_HOME property, so it can find its own PATH.
See how you get on with that, and good luck with it
By the way: I have never installed Eclipse. It is an executable jar and you can unzip it and save it to a folder and double-click the round blue icon called Eclipse.exe and have it run on Windows. You can edit an application launcher to start it on *nix. Don't know about Macs.