A lot of people have been asking me lately: What's the difference between Blu-ray Disc and HD-DVD? Most of the time I try to explain how they work and how it affects people, etc. For the last time (...yeah, right): Both offer 1080p video and high-end audio quality (Dolby digital, THX, 7.1, etc). If you don't own a High Definition TV, forget about it, you're going to waste that money on that type of player. At least you'll need a screen that can support 720p video (1080p been ideal) and at least a component connection (again, HDMI is the ideal). If you only have a old CRT TV, not even with a composite connection you are asking the wrong question. You need to ask if you need to upgrade your TV.
Anyways; the mayor difference, my opinion of course, is the storage capacity. The Blu-ray disc can hold 25GB per layer and the HD-dvd 15GB. Let say that both disk are dual-layer; then, the Blu-ray disc will hold 50GB and the HD-DVD disc 30GB. After that, is also good to know that the less expensive Blu-ray player on the market is the Sony PS3 and the less expensive HD-DVD player is the Xbox360 HD-DVD player add-on. For more details check this link out, and if you're not satisfied check this other link. In the meantime, NO MORE QUESTIONS ABOUT THIS SUBJECT PLEASE.