Check the motherboard. You can connect two drives to a single parallel cable. Most traditional motherboards have two IDE sockets and you can run a maximum of four drives. (one cable per socket, two drives per cable) but you need to configure the drives with jumpers as "primary" and "slave".
Many of the newer motherboards have a "SATA" (Serial ATA) socket or some combination of SATA and IDE but you'd have to use a SATA drive with a SATA cable to use the SATA socket.