Have you enabled printer and file sharing on the XP machine?
Have you installed the printer in your laptop? this would need to be installed as a network printer on the laptop and connecting to the XP machine,
The printer might be trying to use the wrong port on your laptop. It needs to know its sending via the network rather than the USB port.
Of cause (and I know you know this, but its surprising how many dont ... the XP machine needs to be on (and not hibernating or sleeping) when trying to use the printer from the laptop.