I have a laptop with trackpoint+three key mouse. Middle button has 'paste' function already. Now, I want to config the middle key also has wheel function which I can press the middle key and use the trackpoint to scroll pages. Opera has this function but I want to setup as a system wide functionality. How can I do this?

you need to edit the xf86config file. Follow these steps:

1. vi /etc/X11/xf86config
2. Browse down to the section

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "PS/2"
Option "Device" "/dev/input/mice"
Option "Emulate3Buttons" "no"
EndSection

3. Press the key 'a'. You will see --INSERT-- appear at the bottom left of the scree.
4. Change PS/2 to IMPS/2
4. Also add another line
Option "ZAxisMapping" "4 5"
5. press escape(esc)
6. Press colon ( : ) and then write 'wq'
:wq

This saves and exits the file and you are all set.

Your mouse section should now look like
Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "no"
EndSection