Install the printer in your XP PC. The simplest way is probably to follow the original instructions, including physically connecting it when prompted.
Then reconnect it again to the Windows 7 Laptop. In the "Devices and Printers" folder, set it as "Shared" by right clicking and selecting Printer Properties and then the Sharing tab.
Make sure that both computers are in the same Workgroup. The default name for Windows 7 and XP Pro is WORKGROUP, but for XP Home Edition is MSHOME.
Then, in the XP PC's "My Network Places", you should have an icon for the Windows 7 PC. Double clicking it shows the shared printer. If you double click that, it should install it as a Network Printer in XP. In the Printers folder, you will then have the printer installed twice - as a Local printer and as a Network printer. Selecting the Network printer, will let you print over the network to the printer attached to the Laptop. Obviously the Laptop has to be running for the printer to be available.