Take a look at Reality Resized in the links. Originally there was a video posted claiming to be Mac OS X Leopard running on their machine, since then it has been taken offline and now there is only a photo. Notable depictions in the video are a tabbed, solid-metal Finder interface, as well as what appears to be slightly more system menu selection effects.
The demonstration was run on an iMac G5 1.6 GHz with 1.25 GB of RAM. While the movie is certainly more promising than last week's fake screenshots, there is no hard evidence that the movie is legit and it cannot independently be verified its authenticity at this time.
Click Here to view the movie as it has been taken offline from "Reality Resized"