HDCD is an encode/decode process which is used with CDs and has NOTHING to do with HD-DVD. Just an FYI.What you will start to see in a few years is HDCD's, Which as you know HDDVD's can hold 40gigs of information.
HDCD has been around since '95. It was an attempt by audiophiles to improve the sound of CD while retaining backward compatibility with ALL cd players.
http://en.wikipedia.org/wiki/HDCD