Reading the excellent blog from RedHill Consulting (http://www.redhillconsulting.com.au/rails_plugins.html), I was not sure of how to install the plugins so I thought I shared the snippets (and post to my blog I use as a public knowlege database).
|ruby script/plugin install svn://rubyforge.org/var/svn/redhillonrails/tags/release-1.1.6/vendor/plugins/redhillonrails_core|
|ruby script/plugin install svn://rubyforge.org/var/svn/redhillonrails/tags/release-1.1.6/vendor/plugins/schema_validations|
Adapt the code for version 1.2 ;-)
Warning I: you should install the redhillonrails_core only once (!)
Warning II: you need to have subversion installed.