Cursor jumps around uncommanded

I have owned a Dimension 8400 almost two years now and just within the last six months a problem has cropped up with my cursor jumping from one side of the screen to the other. Sometimes this occurs when I am actively using the mouse, and other times it happens on it's own. Also, it almost always jumps from the right side of the screen to the extreme left. What started off as an infrequent nuisance has evolved into a very frequent aggravation. Is there any help for this problem? Thanks!