|I don't think you need to remove the touchpad. Is that the only listing in Device Manager for pointing devices?|
I don't use laptops but I think you need to use an Fn key or something to enable an external mouse. Could be wrong about that though.
OK, I just tried connecting a USB optical mouse to my system along with my already working PS/2 mouse. The result was WinXP found and configured the USB mouse.
There is ONE cursor on the screen and EITHER mouse can move it. The USB uses no additional resources other than what the USB ports already use. My PS/2 mouse is using IRQ 12, which is the default for a PS/2 mouse.