A new split editor prototype that is integrated into the Eclipse workbench API has been available as a patch on the Eclipse Bugzilla for some time now. Unfortunately, I have not able to create an easily deployable plugin that can be installed easily in any Eclipse 3.4 distribution (by copying to the dropins or plugins directories). Even if I did I would probably have to worry about the legal aspects of redistributing Eclipse code, since the plugin will no longer only contain my code.
That said, you can test out the latest split editor by checking out the o.e.ui.workbench project in Eclipse, applying the patch from bugzilla, and debuggin Eclipse from Eclipse. There are no immediately visible changes, but it would be very helpful to have as many people as possible test the split editor in everyday use. I do not expect a lot of users to go through the above procedure, however, and so I will keep trying to get an easily installable package out.
Next time I will talk about the internal integration design of the split editor because I believe this is the most interesting part of all. This will be of particular interest to Eclipse plugin developers who want to know how to enable editor splitting for their custom editors.