If you have no video in, then you need a different TV. Not true. Just use an RF converter. They work great. They automatically sense when your DVD is on. Otherwise, they pass your cable signal through. And, they are inexpensive.
http://www.walmart.com/catalog/product.gsp?cat=3996&dept=3944&product... or
http://tinyurl.com/td4j Philips RF Modulator PH61159 $17.84 USD -Works with DVD p_layer_s, VCRs, WebTV systems, video game consoles, camcorders and digital cameras -Automatically switches from a TV channel to the video product that you have connected -Operates on Channel 3 or 4 on your TV set -RF input and output -Stereo audio inputs -Composite video input