Try out Enlightenment. It's REALLY nice, and VERY easy to make it look like OS X. And you don't need much in the hardware arena for it to work right either. I've gotten some of those screen shots of mine with Enlightenment E-17 with Slackware, running on a REALLY crappy machine.
The specs of one of those desktops, are this:
Intel Celeron @ 433 MHz
192 MBs of RAM
8 MB ATI crap video card
And that was more than enough to run Enlightenment E-17 with not only the Rain FX where you have clouds and Rain Drops falling on your desktop, but also, Snow on it, and even Fire and Flames at the bottom, all of which have neat special FX, and on top of that, the Flames looks like real ones. They move and do things like real Fire lol.