The easiest way to do it is to utilize an RF Modulator. They are available from $10 – $30 depending on how many items you think you may need it for. The purpose of the device is to convert Audio/Video outputs (yellow, white, and red cables) to a coaxial connection on older televisions. Basically all you do is connect the cables from your DVD player into this device and then run a coax cable from it into your television, then put your TV on CH 3 to watch a DVD movie. Some people get confused by these because they already have a cable going to the coaxial jack on the back of the TV. Not to worry. The RF modulator will have an input for that connection as well. So you will connect your DVD player with the Audio/Video Cables, then connect your Cable Box (or VCR or Satellite or whatever else was connected to that jack originally) to the coaxial input on the RF modulator. Then you will have one cable going from the RF modulator to the TV. When you want to watch a DVD turn the TV on to channel 3, and hit play. When not watching a movie you just turn off the DVD player.
I hope this helped.