For PHP development, I use Eclipse and the PDT Plugin. I always use the "update manager" functionality of Eclipse to install my plugins. PDT has some dependency issues, so here's how to get it installed...

First, add the following update sites...

- EMF - http://download.eclipse.org/modeling/emf/updates/releases/
- GEF - http://download.eclipse.org/tools/gef/update-site/releases/site.xml
- PDT - http://download.eclipse.org/tools/pdt/updates/site.xml
- WTP - http://download.eclipse.org/webtools/updates/

The dependency chain goes as follows:
PDT -> WTP -> GEF -> EMF

Start by installing the EMF plugins required by GEF...

EMF -> EMF SDK 2.3.2(EMF + SDO + XSD)
- Eclipse Modeling Framework (EMF) - org.eclipse.emf.common
- Eclipse Modeling Framework (EMF) - org.eclipse.emf.ecore
- Eclipse Modeling Framework (EMF) - org.eclipse.emf.edit
- Eclipse Modeling Framework (EMF) - org.eclipse.emf.ecore.edit
- Eclipse Modeling Framework (EMF) - org.eclipse.xsd.edit
- Eclipse Modeling Framework (EMF) - org.eclipse.xsd
- Eclipse Modeling Framework (EMF) - org.eclipse.emf.edit.ui
- Eclipse Modeling Framework (EMF) - org.eclipse.emf.common.ui

Second, install GEF...

GEF -> Eclipse DSK R3.3.2 -> Graphical Editing Framework

Third, install WST...

WTP -> Web Tools Platform (WTP) -> Web Standards Tools (WST) Project

Finally, you can install PDT...

PDT -> PDT Features -> PDT Feature