Hi Nigel,
What your looking for is an OSGi bundle, the Eclipse Equinox project maintains these. You can download these OSGi bundles from:
http://download.eclipse.org/equinox/(Spent the last ten minutes trying to find the Equinox p2 site, but couldn't, which is ironic seeing as though p2 itself is also a sub project managed by the Equinox team. You think they would 'advertise' their p2 repo more openly?)
Anyway download the equinox bundles and use these for building your target. For working with targets see:
http://www.modumind.com/2009/09/01/creating-an-eclipse-rcp-target-platform/John