You should be able to keep using your old Parallel interface under Vista but you will need to change the PortIo.dll.
vista and XP has blocked direct port access, you need to communicate directly with the operating systems kernel. Jan Alexson's web site www.lvr.com will have the new parallel port driver available. As for hardware just purchase a USB to Parallel converter lead. If your application works on XP then simply using this lead should get you going again.. Try www.cpc.co.uk or similar for this lead

J.