Jumpy mouse pointer

[Bill Planey]

For some time I've had problems with my mouse pointer jumping to some
far-away point on the screen, usually the bottom left corner, when I am
doing practically anything.  It happens at seemingly random moments - I
could be attempting to navigate to a choice on a submenu, or just moving
from one spot to another, getting ready to click on a button, or dragging a
selection marquee... Then boom, the pointer is completely somewhere else.

Apple heard me describe this problem when my computer was still under
warranty, and they sent me a replacement Pro Mouse. It never really went
away, but it seems to be happening more frequently since upgrading to
10.2.6.

My system: TiBook 400 with 512 mb ram and 10 gig internal drive. Both USB
ports occupied (keyboard/mouse takes one, Canon scanner the other). I do not
have a USB hub.  This system does occasionally fail to recognize an item
plugged into the USB port - so, for example, if it won't recognize the
keyboard plugged into the left USB port, shifting it over to the right one
will usually allow the keyboard to be recognized.  That has happened with
more than one keyboard and the scanner and the mouse, so the device itself
cannot be faulted.

Anyone have any ideas why this is happening?

Thanks,

Bill