Problems getting all buttons in intellimouse working using imwheel & xmodmap

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

I'm trying to get the side buttons working on my ms intellimouse under
sarge.  Previously under yoper, I had set XF86Config-4 to a 7 button
mouse with ZAxisMapping to "6 7", run xmodmap -e "pointer = 1 2 3 6 7 4
5" and then run imwheel to map the side buttons to something useful.
However this isn't working under sarge.  Here's where I'm at:

I'm running on a laptop with a touchpad & a MS intellimouse attached by
USB.  The mouse section of XF86Config-4 looks like this:

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

The odd thing is that the touchpad doesn't work atall, and
the /dev/psaux device seems to be my USB intellimouse - since changing
the original config of the /dev/psaux mouse from 5 to 7 buttons caused
the scrollwheel on the intellimouse to stop working.

So, question 1 is why does the USB mouse show up as /dev/psaux and can I
change this?  Could this be the cause of my problems (below)?

With this setup xev shows the following button mappings:

left mouse = button 1
click scrollwheel - button 2
right mouse = button 3
scroll down = button 7
scroll up = button 6
left side button = button 2
right side button = button 3

I then run xmodmap -e "pointer = 1 2 3 6 7 4 5"

Now, xev shows left, right & scrollwheel clicks to be the same.  However
the scrolling down now shows as button 7, then if I carry on scrolling
button 5.  Likewise scrolling up shows initally as button 6 then, if I
carry on scrolling, button 4.  The side buttons still act as buttons 2 &
3.  Obviously running imwheel doesn't work because the button mappings
are still messed up.

As an experiment I tried changing the protocol to ExplorerPS/2.  This
time before the xmodmap line, the side buttons acted as buttons 4 and 5.
However after running the xmodmap line, a single scroll up gives a
press/release of both button 4 & 6.  A single scroll down gives
press/releases of buttons 5 and 7.  The side buttons give the same
events as a scroll up or down.

So, why does the xmodmap line not work?  And why does scrolling activate
as 2 buttons?