Assuming that your cable box has HDMI output as the only option and your TV doesn't have HDMI you will need to convert HDMI to a compatible video and audio output. If the TV has a DVI-HDCP then you want to convert HDMI to DVI plus audio.
If it has component video then convert HDMI to that plus audio. If you only have composite video then convert HDMI to that plus audio. You can't use a passive cable to do this.
I would contact my cable provider before buying a converter to find out if they have any boxes with compatible outputs for your TV.