Activate the 4 finger gestures on a MacBook Air Rev 1

One of the most practical things of the new trackpad of MacBook Pro, MacBook and MacBook Air, is the support of 4 fingers gestures that allows the use of expose and is very practical on screens of small size.
Alas, this is not possible on the old MacBook Air. Members of the forums discovered that this limitation is not due to hardware, but software. By forcing the installation of certain system libraries on MacBook Air V1, they succeeded in activating this function. We will not describe the method here, because it requires not only the access to the system on the new portables, but also to modify these libraries by hand and this presents a significant danger that may result with a machine unable to start up again.
It remains only to wish that Apple disregards its current meanness and with the 10.5.6 update enable these advanced functions for these trackpad on all the machines that have adequate hardware.