The delta pack is required to use PDE/build.

This deltapack contains the platform specific features and plugins which are required for building Eclipse product for all platforms. It also includes binary launchers for all platforms in the feature "org.eclipse.equinox.executable".

The deltapack can be found http://download.eclipse.org/eclipse/downloads/ . Select the release for are interested in, e.g. 3.5 and search on the page for "Delta".

Extract the delta pack to a new directory, I recommend to use eclipse install directory and then "/deltapack/eclipse/". So if you installation directory is c:\eclipse35 then it should look like the following.

To make the delta pack available to the Eclipse IDE add it to the target platform under Windows-> Preferences-> Plug-in Development -> Target Platform. Edit the exiting target platform and add the directory of the delta pack to it.