Just in case anyone was stumped like me.
Instead of the usual (XP) add network printer/browse for printers etc, you have to add a new local port, the port name has to be \\server\sharename (note sharename not display name), then install the driver as prompted.
Instead of the usual (XP) add network printer/browse for printers etc, you have to add a new local port, the port name has to be \\server\sharename (note sharename not display name), then install the driver as prompted.