There's some great advice here: http://ubuntuforums.org/showthread.php?t=1419833
Easiest solution is probably just:
- Go to System/Preferences/Mouse
- Click on the touchpad tab and you can select two finger scrolling under the scrolling heading.
If that fails, you may need to do something like shown below, depending on your hardware:
xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Two-Finger Scrolling" 8 1
xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Synaptics Two-Finger Scrolling" 8 1 1
xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Synaptics Two-Finger Pressure" 32 10
xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Synaptics Two-Finger Width" 32 8
You've gotta run at least these four (more in the link above), and you have to run them on boot, so you'll probably want to drop them into a startup script; preferably one late in the boot process.
I'm not sure what make of touchpad you have, so you may have to do a little digging to get the right names and properties to set.
To check your input devices for the touchpad, run
xinput list and look under the pointer section. You should have multiple items in the list, and the one with highest id is likely your touchpad. If it's synaptic, you're golden, and the four commands above will solve you woes.
If not, you must dig a little.
In The second column of xinput list, each device has id=#
xinput list-props #, where # = your device id.
This will show you all the available properties for your input device.
The commands above differ from my default settings from the return values of xinput list-props in that the 8s and 32s describe the size of the data being set. The second and third ints match exactly what xinput list-props returned, but going through the act of setting enabled two finger scrolling for me.