Wild scrolling when I move the cursor on the trackpad?

How do I stop the window from scrolling wildly when I move the cursor on the trackpad?

I am running Windows XP SP2 on an Inspiron 2200 laptop. It happens intermittently, perhaps when my finger is a little heavier on the trackpad. It sort of looks like Windows is responding to a phantom scroll-wheel. The window scrolls in the opposite direction to the cursor movement when the cursor starts on or near a vertical scroll bar. The amount of scrolling depends on how far vertically I move the cursor. It is definitely affected by the direction that I start to move the cursor in, and less likely when I start moving horizontally. [That is the usual case -- it also can do horizontal scrolling if near a horizontal scroll bar.]

One other clue is that sometime it displays a small icon like 3 boxes in a row with arrowheads in the end boxes.

Any ideas?

-- Allan