You need 2 resistors, 2 zener diodes, and a DB-9 female connector. I presume you already saw unicron's diagrams. The old serial cable was to recycle the DB-9 connector. The IDE cable was to recycle the wiring. If you want to cut down on the cost of the PCB/breadboard, you could solder the correct parts and short them together assuming you are good with the soldering iron like what this guy did:
http://mail.exis.net...kus/item_77.htm.
I'm bad with the iron so I had to use the breadboard as an easy way to connect the parts together. A multimeter is useful to have to check continuity. btw zener direction (orientation of the dark strip) matters.