Then, run the following command:
xinput --set-int-prop "USB Mouse" "Evdev Wheel Emulation" 8 1
xinput --set-int-prop "USB Mouse" "Evdev Wheel Emulation Button" 8 3
Now, holding the right mouse button and moving up and down will scroll. Very useful for reading long articles.
Requirements: evdev 2.1, X server 1.6 and xinput 1.4.
You can do the same in a permanent manner by merging the keys input.x11_options.EmulateWheel and input.x11_options.EmulateWheelButton your HAL fdi file. Check the evdev man page, there's a few extra tweaks related to wheel emulation.