Ars Technica has the story on the effort by KDE to port a great deal of its environment to run as native* Mac applications: “KDE goes cross-platform with Windows, Mac OS X support”.
More project details as well as torrent files are on the KDE TechBase, here: “Projects/KDE on Mac OS X”.
Mac OS X is already a “desktop environment” in the sense that it provides window management, application launching, etc. The goal of KDE on Mac OS X is to provide the rich frameworks and applications in KDE to a wider audience.
The Installation section of that wiki page notes:
You must install at least Qt, kdesupport, and kdelibs for any of these packages to work. Also, kdepimlibs, kdebase and strigi are recommended since a number of things will want them. (…and it has Konqueror)
Amarok (which I’ve seen a lot of people mentioning they were excited about getting) is “temporarily not building” so isn’t included in the downloads.
* - for certain values of native ;)