In Windows XP go to Start/Control Panel/Mouse/Pointer Options tab, uncheck the box for the "Snap To" feature. Click apply, OK. That may solve the problem.
I bought a mouse once that did this. Turned out to be built-in feature of the mouse that I couldn't disable.
Best of Luck
I use a Logitech ball mouse, installed about 6 months ago on a newer Compaq machine, running XP.
The mouse cursor seems to have a life of its own and moves upward on the screen when I'm not touching it. I have to keep my hand on the mouse to keep it where I left it. I've done virus scans, etc, but nothing comes up.
Ideas? It's sort of creepy.