This is a good mouse and it's definitely supported as an IMPS/2 device. Microsoft really should stick to what they do best: input devices.

Here is part of my XF86Config generated by RedHat:

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "no"
EndSection

Section "InputDevice"
# If the normal CorePointer mouse is not a USB mouse then
# this input device can be used in AlwaysCore mode to let you
# also use USB mice at the same time.
Identifier "DevInputMice"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5"
Option "Emulate3Buttons" "no"
EndSection

I haven't tried mapping the exta buttons to do anything useful yet but I have used it with a PS/2 adapter before and it also worked fine.

The hardware works, but the software doesn't detect the side buttons without additional modifications such as the iwheel program

(Bought in 2001, hence the high price paid)

Works fine with Slackware. To get the side buttons and scroll to work properly, this is my /etc/X11/xorg.conf entry:

Identifier "Mouse1"
Driver "mouse"
Option "Protocol" "ExplorerPS/2"
Option "Device" "/dev/mouse"
Option "Buttons" "7"
Option "ZAxisMapping" "6 7"

And my /etc/X11/xinit/.Xmodmap entry (this could be ~/.Xmodmap if you want):

pointer = 1 2 3 6 7 4 5

If you want to reprogram the buttons, then you will need additional software.