Boris,
I/the installer uses Eclipse 3.6.1. I'm not eclipse expert, but from what I see from the ant build script, you need to download several files and extract them over eclipse installation.
The jBPM (modeller) package is jbpm-5.0-SNAPSHOT-eclipse-all.zip located here
I'm not sure about the dependencies however... the installer installs efm, efm transaction, gef and gmf as well. You can find the URLs easily, when you download the installer and look into build.xml and build.properties files respectively...