Many laptops hardwire an internal switch so that a PS/2 mouse can take control when connected (thus disabling the pad or stick), and the pad (or stick) takes control back when the PS/2 mouse is disconnected. This ensures that there's always one, and only one, working mouse device (seems natural at first glance).
So if you want to have several pointer devices, you'll have to try configuring both in your X config file (one as a pointer device, the other as an events sender, from what I've read on MUB1). If this does not work (it would not with my laptop), you may have better luck with an USB mouse, as this port cannot be hardwired to a switch (IMHO, because much more than mice can be plugged to USB).
Yves.
