You don't have to install anything, you just view it using your browser.
Windows:
Firefox Beta - http://mzl.la/gnnLFP
Chrome Beta - http://bit.ly/xckw8
Mac:
Safari - http://nightly.webkit.org/
Chrome - http://build.chromium.org/f/chromium/continuous/mac/LATEST/
Linux:
- Linux 32-bit: http://build.chromium.org/f/chromium/continuous/linux/LATEST/
- Linux 64-bit: http://build.chromium.org/f/chromium/continuous/linux64/LATEST/
After downloading the browser, enable WebGL: type about:config into the address bar, search for "webgl", and double-click "webgl.enabled_for_all_sites" to set it to true.
Chrome Install:
Should work out of the box!
Once you have installed either browser navigate to http://bodybrowser.googlelabs.com/ and enjoy!