I was able to solve the usb mouse detection problem by installing knoppix on my hard disk, set up gpm with the following configuration options: <gpm.conf>
device=/dev/input/mice
responsiveness=
repeat_type=raw
type=autops2
append=""
sample_rate=
</gpm.conf>, and by changing the XF86Config-4 file in the sections <ServerLayout> InputDevice "USB Mouse" "CorePointer"
</ServerLayout> and adding a new <Section "InputDevice">
Section "InputDevice"
Identifier "USB Mouse"
Driver "mouse"
Option "Device" "/dev/gpmdata"
Option "SendCoreEvents" "true"
Option "Protocol" "auto"
Option "ZAxisMapping" "4 5"
Option "Buttons" "5"
EndSection
<Section "InputDevice">.

I have also automated this procedure adding a few symbolic links:
/etc/rc0.d/K20gpm -> ../init.d/gpm
/etc/rc1.d/K20gpm -> ../init.d/gpm
/etc/rc2.d/S20gpm -> ../init.d/gpm
/etc/rc3.d/S20gpm -> ../init.d/gpm
/etc/rc4.d/S20gpm -> ../init.d/gpm
/etc/rc5.d/K20gpm -> ../init.d/gpm
/etc/rc5.d/S20gpm -> ../init.d/gpm
/etc/rc6.d/K20gpm -> ../init.d/gpm

cu, g.