Under normal conditions I would check /etc/X11/xorg.conf ....
but since there is no such nice config file unter maemo that I know, it seems not possible to get a mouse working.
And its not only that you cannot see the pointer. Its that the mouse is not associated to an input device. So maemo doesn't know what to do with the information from the usb mouse and pipes it to /dev/null

If anyone has some usefull information about this topic it would be cool to read them

I'm about to go on hollidays and the N770 will be my only computer during that time. A mice and a small keyboard would be very very cool to have...

Timo