I've been thinking about something that just might work for non SSE2 processors. The idea is this: take Darwin, add KDE (or another desktop environment), copy the OS X top bar and then add the real OS X dock and finder. It would take some work to make the apps work with KDE, but it's possible isn't it? After all, you can install KDE in OS X. I know that some of the apps don't support processors without SSE2, but isn't there a work around?

Maybe we could use this: http://www.xdarwin.org/

Then it wouldn't be real OS X. No point in that, its just about as good as a visual theme, and there are tons of those already.

The point of it is being able to use OS X sofware and have the interface of OS X.

It won't be able to use OS X software, it will be able to use Darwin software but not OS X software. Darwin doesn't equal OS X. Also that XDarwin you liked to seems like software that runs on OS X, similar to Fink. It doesn't run on Darwin.

Really? Someone else told me that Darwin, being the OS X kernel was 100% compatible with apple software (like iLife.)

No, it isn't as far as I know. I'm almost 100% sure of it because OS X software uses technology like Quartz, Carbon, Cocoa, OpenGL, etc. none of which is in Darwin. OS X is basically Darwin, layered with Quartz, Cocoa and all that stuff and then the Aqua GUI on top. Look here for a brief explanation of Darwin and what role it plays in OS X. So basically, unless it apps are coded in a language that has full Darwin compatibility (which no app as far as I can tell does) there is NO WAI.

iLife for sure you can't run on Darwin. Oh yeah and why would Apple make Darwin freely available if you could run all your OS X apps on it?

Yeah it's not that easy, darwin is the brain and OSX can't live without it, but without all the other organs of the body there's nothing much you can do. Only terminal style apps would work, if they don't use any other framework.

Well, then why wouldn't it work to install the framework and use KDE? Does the framework require SSE2?

For a project is a good idea....BUT.... the sse2-less cpu's are way old (pre 2004) I think that new technologies relies heavy on the computational power and simd instructions code. We're now on post sse3 instructions...

Those frameworks only work with the darwin kernel, not KDE, and they are closed-source so can't be ported. The darwin kernel needs at least SSE2. The story ends there. Anyway porting those frameworks would be like porting the entire OS.
The less complicated way would be to make a SSE1 darwin kernel, it would be a lot of work, and far too slow.