Madcow 2.0 is a complete rewrite to decouple Madcow from WebTest, and to be based on a more generic 'blade-runner-plugin' framework, currently targeted at WebDriver.
Check out the awesome documentation at http://madcow.4impact.net.au now and get testing!
As this is currently in development, it is prone to breaking and changing alot :)
For the existing (rock-solid) Madcow, see https://github.com/4impact/madcow-classic