I had exactly same problem. tried tons of things, among others recompiling kernel with custom DSDT.
Finally - all it took was:
echo -n "psmouse" > /sys/devices/platform/i8042/serio0/drvctl
i have found it at http://kerneltrap.org/node/4269
After issuing this command touchpad is recognized by kernel (seen in dmesg).
you can put this in your rc.local