See the InputDevice section of your /etc/X11/xorg.conf file for text\r\n
Driver "synaptics"\r\n\r\nGoogling around, it looks like the touchpad doesn't use the synaptics driver but an Apple specific one. This [link|http://users.linpro.no/janl/hardware/tibook.html|page] has a section on what needs to be done to emulate the middle and right buttons using keys F11 and F12. See the heading "Mouse button emulation".\r\n\r\n
Hope that helps!