From the Thinkwiki:
Modern distributions like Ubuntu 8.10 and Fedora 10 use HAL to configure the input devices. You should no longer make changes to xorg.conf as by default Xorg (through the evdev driver) will let the kernel now handle input devices.
But before you get started on this you should make sure you have all the updates applied from your distro vendor as both Ubuntu 8.10 and Fedora 10 require some additional fixes that you will need.
By default the middle mouse button is that, a middle mouse button, which in Linux is used for the Paste operation.
But you can configure it to act in the same way as in Windows, such that you can use it for vertical scrolling (keep the button pressed and move the TrackPoint up and down to scroll). To accomplish this create the file /etc/hal/fdi/policy/mouse-wheel.fdi as root with the following content:
<match key="info.product" string="TPPS/2 IBM TrackPoint">
<merge key="input.x11_options.EmulateWheel" type="string">true</merge>
<merge key="input.x11_options.EmulateWheelButton" type="string">2</merge>
<merge key="input.x11_options.YAxisMapping" type="string">4 5</merge>
<merge key="input.x11_options.XAxisMapping" type="string">6 7</merge>
<merge key="input.x11_options.Emulate3Buttons" type="string">true</merge>
<merge key="input.x11_options.EmulateWheelTimeout" type="string">200</merge>
After this reboot, or restart the hal service and Xorg. You can validate the settings with lshal.