Let me just say, spend the 5 dollars more for the logitech or the basic microsoft optical... kensington is UTTER CRAP... first of all this is a true ergonomic nightmare, who ever designed this thing must have been a complete moron. 2nd, the drivers are pathetic, there are well noted problems of the wheel mouse. 3rd, on my p3-500 system, my computer would not even BOOT up to windows with the usb mouse plugged in... unplugged and it would boot. My brother tried it on his system and was able to get the mouse installed but the wheel functionality would constantly dissapear. I have a microsoft intellimouse optical on my main machine and its a dream come true. works perfect.
edit : I've had 2 previous usb kensington mouse in a box... they both broke within a 3 month period... the 2nd was a replacement for the first. I will never buy a kensington product again.