This is a procedure that I've had success with installing Vista printers when the normal install didn't work.
- Temporarily connect the printer to the Vista machine and install it as a local printer using the proper Vista drivers.
- Disconnect the printer and move it to the XP machine it normally connects to and make sure that it's configured as a shared printer.
- Open the Printers and Faxes folder on the Vista machine, right click on the printer and select properties.
- Create a new Local Port for this printer with a name of the full network path name to the shared printer, i.e. \\computer_name\printer_name.