Composite RCA will be better than a coaxial cable (RG6).
The order of quality and maximum resolution from best to worst is:
HDMI (including HDMI 1.4 3D)
DVI
Component Video
S-Video
Composite
Coaxial cable
Yes. HDTV signal can be used through HDMI, use the Component connections (not to be confused with composite) if your set has it, if not, then s-video and video would all be better than Coaxial cable.
There are many converters on the market, from a few dollars to many thousands of dollars for a studio quality decoder. There is a limited benefit in using a dedicated composite to component decoder: Once a signal has been encoded into a composite or an S-video signal, some of the picture detail is lost forever. Decoding the signal into component does not restore the quality. Bear in mind that every television that has a composite or S-video input has a decoder to obtain a component signal. Using an external decoder simply moves the process to another point in the signal path. Having said that, a good quality decoder may give better results than a television's internal decoder.
A coaxial cable sends all signal down one line. All the color, brightness and audio is piped together to the television, where a signal converter is required to separate all the information to be displayed on screen. An audio/video, or RCA cable (Red-White-Yellow), separates the signal into three parts, video, the left audio channel, and the right audio channel. The TV then has to only convert the video signal into the colors and brightness. Since the audio is already separated from the video with the audio/video cable, there is one less conversion needed at the TV. This allows for better picture quality with audio/video cables. To put a number to it, audio/video cables give 20% better quality signal that coaxial. S-video is even better as is separates the video signal into color and brightness. Component is better yet, as it separates the colors from each other (Red, Green, Blue) and sends the brightness with the green signal. These are all analog methods of providing a television with signal. Digital methods like DVi and HDMI provide the best signal quality of all.
The Dell Inspiron 4000 does not include a coaxial jack. Unless you are using a third-party add-on, you are most likely confusing the S-Video jack / cable with coaxial. S-Video is used for outputting high-quality video to newer televisions. It does not, unlike coaxial cable, carry an RF signal.
coaxial
The picture is slightly better in some circumstances because the S-Video separates the brightness and color signal from the source on two conductors in the cable. The resolution is the same, and does not effect the audio quality. If your TV has only S-Video or composite connectors, you may notice no difference in the quality of the picture. The big steps in quality upgrade come when you use a component video or HDMI cable.
Coal and Iron elloc72
A single cable carrying video will be carrying a composite video signal. This signal has brightness and two color signals encoded into a single signal. To generate a component signal (YPbPr)a video decoder is required. They are available from many sources from low cost domestic units to stunningly expensive broadcast models. The better the decoder, the better the resulting image. It is very important to understand that a composite signal has suffered losses because of the encoding. Decoding the signal to component does not restore that quality. Component interfaces can handle high definition as well as standard definition signals. Decoding a composite signal will result in a standard definition signal. Connecting it to a high definition input will not result in a high definition signal. Normally, the only reason to decode the signal to component is to interface to a device that only accepts component signals.
A composite signal is a mux or a bus signal. These can be thought of as a collection of other component signals.
coaxial
Coaxial
The purpose of a coaxial cable is to act as a transmission line for a radio frequency signal. The electromagnetic field carrying that signal exists only in space between its inner and outer conductors.