Mac Client Release Notes
If the download does not start automatically you can click here to download v3.0.1.
Open the DMG, then double click to install (requires 64-bit OSX 10.6 or better). It should select itself as your current screensaver, or you can open the System Preferences / Desktop & Screensaver and choose "Electric Sheep" from the list on the left.
If you have trouble, see the help page.