The simplest way to install PHPEclipse is to use the PHPEclipse update site.
If you are using Eclipse 3.2 you will want to use the following URL for your update site:
http://update.phpeclipse.com/update/stable/1.1.x
For Eclipse 3.3 and 3.4 use
http://update.phpeclipse.com/update/stable/1.2.x
For Eclipse 3.5 and higher use
http://phpeclipse.sourceforge.net/update/indigo/nightly