I was wondering when someone else was going to post a msg with this problem. I have had 3 systems that the mouse went beserk on. All of them have been PS/2 mice. It occurs randomly for no apparent reason. The mice would lock, jump randomly, and not just a skip. I have since attached optical usb mice to these systems and all is fine. The mice (ps/2) in question works fine on W98/W2K systems that I have tested them on. I just gave up on trying to get them to work under XP.
I am not saying that PS/2 mice will not work under XP. This is just what I have encountered on 3 systems. One system being mine and 2 at work.