X configuration might need change, I had to change mine:
2.4.x Option "Protocol" "MouseManPlusPS/2"
2.6.x Option "Protocol" "ImPS/2"
however my side button (button 6) does not work. The other options is
to use evdev driver (I haven't tried it yet):
Option "Protocol" "evdev"
Option "Dev Name" <dev name>
not sure what exactly would work for you, the way mouse works is a lot
different in 2.6.x (instead of raw device kernel recognizes mouse
itself, however the device reacts differently depending on which
protocol you use to communicate with it).
search debian-devel for 'logitech mouse [was: Lost Trust]', messages
from 2004/5/31 - 2004/6/8 (read the whole thread, some messages are not
relevant to your problem but some of them are quite informative, like
the one that mentions evdev).