Also, based on the Dependencies listed on that page, I upgraded to Eclipse 3.5 (for Mac OS/X) and also downloaded EMF 2.5 (although it appeared to already be a part of Eclipse 3.5). My Eclipse 3.5 install seems to work (not sure if there is some way to verify EMF).
I didn't see any install instructions for DLTK, so I just copied the contents of the "features" and "plugins" folders to my Eclipse features and plugins directories and restarted Eclipse.
I don't see any DLTK Ruby capabilities in Eclipse, though. In particular, I was looking for a Perspective or a some Ruby options in the Eclipse Preferences. Nothing at all. No errors that I can see. If I look in the installed software, I do see several DLTK entries, though.
Is there some other install procedure I should follow?