Have a look at this pic...




top section is s-video with separate audio

next is coax.. audio and video combined

next is composite.. one video and two audio

at the bottom is component and two audio.

(this pic shows two of everything so don't let that confuse you. It's all I could find quickly)

So, if you're running composite then the cable you got from radioshack is probably ok. 3 rca is all you need in total and it seems to be what you have/need.

If you want to run component you'll need 2 more video quality rca cables but it sounds like that's not what you want.