I have an eclipse installation from the "Eclipse for PHP Developers" package and I want to "extend" it to have in addition to the PHP components all the components of "Eclipse IDE for Java EE Developers". but the Feature Lists in the above links do not match the items I am presented when I choose "Install new software..." from the eclipse help menu.
Is there anything I can do about this?
the result of copying plugins/features into that folder is not that predictable and hence not safe. Eclipse adviced to install plugins via "Install new Software" - it will tell you about conflicts (like different plugins use different version of another plugin" etc; or you need to install another plugin etc.) Otherwise I had situations when it didn't work and I got no idea why (had to read logs to figure it out).
Well, to install new plugin you have few possibilities:
1) "Install new Software" - you already tried it. Take into account that the list of plugins by default is limited here. But below the button "Add..." you can see "Available Software Sites" - this list is enhanced, and some of plugins you can find here". UPDATE: the process of installation is described here
2) With new Eclipse (Helios) you got new way to add plugins, so called Eclipse Marketplace (Help/Eclipse Marketplace...). This is recommended way to look and install new plugins.
Back to your problem - I think it is much more easier to download Java IDE for Java EE Developers, and install PHP Development Tools there. In Marketplace I selected Yoxos as source, typed "pdt" and found plugins related to PDTs (although I'm not sure there are all parts of it)