what is the difference between hd composite wires and hdmi cords? which is better? sound wise too?

As for sound, HDMI has the capability to carry digital audio signals as well as Video, and there may be some forms of high res surround it will carry that may not be available on other types of digital audio connections...but at this point, there is no difference. Also, HDMI standards are in the process of changing. The standard that you'll need to get the high res surround signals is HDMI 1.3. Problem is, few components have HDMI 1.3 (they are just now being released) and few older units will be upgradable to the newer standard. 5 years from now, it will be nice to have a single cord that carries everything between equipment...but those days aren't here yet. The easy way to determine if your preamp/reciever will accept the digital audio stream thru the HDMI cable is to check to see if your Preamp/reciever has the option of selecting HDMI as the digital audio source for the input you are using...such as DVD. If it doesn't, you'll need to run a Coax or Toslink digital (I prefer GLASS Toslink for my digital connections) cable to your AV preamp/reciever from your source (DVD, Cable Box, Tivo, Sat reciever, etc).

Component video is strictly a video only standard. If you use it, you'll need to run an additional digital audio connection from your source to your preamp/processor/AV Reciever. That can be in Toslink Optical or Coaxial Digital form. Standard home video comes in six basic formats, in order of resolution (picture quality) from Standard Definition (480 Interlaced) to High Definition 720 Progressive/1080 Interlaced)