yes, i used to have the same problem.
is your mouse a microsoft intellimouse thingy?
anyway, open up your XF86Config file, it should be in /etc/X11/ .
go down to the section that refers to the mouse
(Core Pointer's InputDevice section)
and then change the line with the protocol on it so it reads
Code:
Option "Protocol" "IMPS/2"
then the line below this make sure that it points to /dev/psaux
this is how mine is set and it all works just peachy :-)
Alex