Whats the difference between hdmi and regular hd a/v cable?

Component HD (Green, Blue, Red) is an analog connection. HDMI is a digital connection. So right there, HDMI is better suited to deliver a consistent, and higher quality, image signal. The digital signal is just transmitting 0's and 1's. There's no issue of signal strength or other such things. Also, HDMI, at least v1.3 (which is pretty much all now), can transmit both audio and video over the same cable. So both audio and video are dilgital. With Component you need separate cables for audio. And you can use a toslink cable for optical audio. So the audio can be made to be of a reasonably equivalent quality. But the video won't be in that case. Most of the time it won't be light years different. But technically HDMI will be better. And if you ever go with an up-converting DVD player or a BluRay player, you want HDMI so you can use all the various types of resolutions available (Some only work via HDMI).