Well, if you don't have another IDE/ATA slot spare, you could either:-
Buy an IDE/ATA PCI card so that you have more slots, then hook up the third hard drive.
or
Buy a SATA PCI card and have a SATA hard drive instead (assuming you haven't already bought the third hard drive?)
In either case they are usually between £10-£20 for them.
or you could just get a USB2 caddy for the drive for around the same price... in my opinion you would be better off with the USB caddy, because then you will have the option of transporting your drive with you to a friends house too if you want to.
good luck with whatever you decide
