Thinkpad Track Point Scrolling
I use the trackpoint instead of the touchpad because I think it is more efficient. To enable middle mouse button scrolling and disable the touchpad I use the following package:
sudo apt-get install gpointing-device-settings
After installation you can open the tool by clicking on System->Preferences->Pointing Devices.
Important: Disable the check box Disable touchpad while typing under System->Preferences->Mouse->Touchpad
Here you can get further information.