To use both a Toshiba laptop touchpad and a USB mouse in linux:

1. Edit the XF86Config-4 file.

"vim" (open vim. press esc to make sure you're in normal mode)
":edit /etc/X11/XF86Config-4"(opens the config file)

2. Under Section ServerLayout, make sure you have:

InputDevice "Mouse 0" "CorePointer"
InputDevice "USBMice" "SendCoreEvents"

(with vim as an editor you need to hit insert to enter 'edit mode' and escape to be in 'normal mode')

3. Scroll down to where the Section InputDevice are. Make the following (the first is the touchpad, the second is the usb):

Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "PS/2"
Option "Device" "/dev/psaux"

Section "InputDevice"
Identifier "Mouse1"
Driver "mouse"
Option "Buttons" "5" (i don't know what this does but many of the google results had this so :P)
Option "Device" "/dev/input/mice"
Option "ZAxisMapping" "4 5" (same.. :P)
option "Resolution" "500" (same..well, in the suse mailing list site anyway..)

4. sources:

Arup Ghose