Touchpad scrollwheel won't scroll under sarge

[rich <stantonrj@cf.ac.uk>]

I'm running sarge on my laptop which has a touchpad & a USB mouse.  The
USB mouse works fine (all 7 buttons!) after using xmodmap.  The touchpad
works fine except for the fact that the sroll wheel doesn't scroll.
Using xev, I see a down-scroll being seen as button 2, while an
up-scroll is not detected at all (left/right clicks are seen as buttons
1 & 3).  Here's the input section of XFree86-config-4:

Section "InputDevice"
        Identifier      "Generic Mouse"
        Driver          "mouse"
        Option          "CorePointer"
        Option          "Device"                "/dev/input/mice"
        Option          "Protocol"              "ExplorerPS/2"
        Option          "Emulate3Buttons"       "false"
        Option          "Buttons"               "7"
        Option          "ZAxisMapping"          "6 7"
EndSection

Section "InputDevice"
        Identifier      "Touchpad"
        Driver          "mouse"
        Option          "SendCoreEvents"        "true"
        Option          "Device"        "/dev/psaux"
        Option          "Protocol"      "auto"
        Option          "Emulate3Buttons"       "false"
#       Option          "Buttons"       "5"
        Option          "ZAxisMapping"  "4 5"
EndSection

The protocol is auto-detected as explorerPS/2.  I also had to manually
modprobe the psmouse module - don't know if this is normal or will have
effected anthing?  How do I get the scroll to work?