Does this apply if it is a track point device? I incorrectly said it is mouse.
"Listen to what I am thinking, not to what I said"
This is common with the Thinkpad track point. I've had 3 different models that all did it eventually. Make sure you've got the latest drivers and you can try adjusting the sensitivity in the trackpoint control panel. I've learned to like the 'touchpad' on my t41 and Santa got me a mini USB optical mouse that beats both hands down!
I believe this is a glitch in the winxp SP2, or so i've been told. I also experience the same thing using an optical and ball mouse. I've tried doing some reading about this and many people have been experiencing this very same problem.