Whoops just re-read original post. I don't believe that there are any PCDP's that decode HDCD.
www.hdcd.com
Pacific Microsonics is the company that started it all. I believe in December of 99 (or was it 2000) they were purchased by Microsoft and that's why WMA9 now plays HDCD discs if you pop one into your computer and use WMA9 as your player.
Everything you wanted to know about HDCD is on the site.
Personally I'm not completely sold that it improves the sound all that much. HOWEVER, having said that I've found that just about every HDCD disc I've ever purchased is quite well recorded. They do produce nice sounding titles and I do recommend picking up a few and giving them a listen. If you visit their website you can see all the titles available on HDCD. Who knows, you might already own a bunch of HDCD titles and not know it. I have a friend who found out he owned about a dozen HDCD titles and didn't know it, look for the little HDCD logo on the back, or just look it up on the website.