Cars 2: The Video Game

To drift, press and hold the  button. The drift strips are the blue arrowed spots on the tracks; later levels have fairly long drift strips. Alternatively, you can just drive as slow as possible while still being able to drift, and slide through a strip without veering off the blue arrows. The achievement pops immediately once you drifted for the required 6 seconds.

In Free Play, you can load up the "Airport Arena" Hunter event. This level has a continuous circular drift strip that you can slowly drift along to easily unlock this achievement. Just come in from the outside, release the gas and drift into the strip. Make minor steering corrections and you can slowly slide over a small portion of the circle for much more time than is required.