Apple ClickPad

Multi-touch gestures like the drag two-finger drag gesture are supported in the current xserver-xorg-input-synaptics package (>1.6.1).

If you would like your touchpad to behave like the natural scrolling mode in Mac OS X Lion, you have to add the next line to your ~/.Xmodmap 

pointer = 1 2 3 5 4 7 6 8 9 10 11 12

For older versions you can check PageFragmentClickPadOld