I am also very confused by all these options.
They say eclipse is a framework upon which applications can be built. So it's like a "transportation vehicle" with varying characteristics: motorbike, car, pick-up truck, and so on.
You need to know what you need, to get what you want or so... I think eclipse.org could do a better job of presenting their products.
For PHP development I have turned away from eclipse and towards the commercial version of PhpStorm from jetbrains. At work we use both eclipse and netbeans, and more and more collegues are dumping eclipse in favor of netbeans (especially after that bloody helios release).
Back in the olden days when I earned my money with Java programming, I had a superb IDE called Together from TogetherSoft. It was later bought by Borland and incorporated into their JBuilder, which by now is also built on top of eclipse I believe. Together was the best IDE I have ever encountered, even after this many years I haven't seen anything close.
Back to eclipse: You can start with the most basic download, and get all the other components by its plugin feature. But sometimes (often?) it is not really clear what a component does, even after reading its description.