This is difficult to answer without more specifics. Coax, Composite, S-Video, Component, SCART, and VGA are all analog; which of these connections does your TV support? I'm assuming the three color cable you have is Red, White, and Yellow, (not RGB) which is composite video and L/R audio. Usually older TVs have either Coaxial input only, or Coaxial and Composite A/V connections. If your TV has multiple inputs then connect your xbox directly to these. If your cablebox is occupying the only input, then you can either use an A/V switch, RF modulator, or the passthrough on your cablebox to get the signal to the TV (depending on your situation). The S-Video and A/V plugs on your cablebox are most likely outputs, passthrough is usually coax only (however, your box may be different).