Curt, a standard RCA cable should work, but I would stronly recommend using a 75 Ohm cable since that is what the SP/DIF standard requires. Normal RCA cables won't hurt your equipment though.
75 Ohm cables are used to transfer video or digital audio.
You should be able to find them wherever audio or video gear is sold.
If you get dropouts:
It might be a good idea to use shielded or double-shielded cables especially if you intend to use it on runs greater than 6 foot. But even if you use shorter runs it might still be preferable because of possible interferences with other pc components (e.g. PSU).