Home theater is in a constant state of technological advancement. For many years, red, white and yellow RCA and S-Video jacks were the standard in home theater. A few years ago, the introduction of the digital HDMI standard made the old analog standard obsolete. The problem is that many people still use devices with analog RCA jacks. Although compatibility is difficult due to HDMI's pure digital, high-definition image and sound quality, it is possible to use an HDMI cable with RCA jacks.
Determine what cables and equipment you need. Since HDMI is an all-digital format, you will need a box that upconverts separate RCA audio/video signals into a combined digital signal. You may also be able to downconvert from HDMI to RCA, but finding a device to perform this task is difficult. Check your local electronics supply store or online resource to find a converter box that is right for you.
Make the connections. Plug in the red, white and yellow RCA cables into your converter box's audio/video input. Plug the HDMI cable into the video output of the converter box, and plug the other end into the HDMI video input of your display device. Do not forget to plug the converter box into the wall, if necessary.
Test the connections. Turn on the converter box. Turn on your devices and tune your display device to the proper HDMI input. If all goes well, you should see an unconverted image with improved quality over standard analog.