De built one of these based on my tracing of the schematic. Look for his posts.
You need a CR563 CD-ROM drive (Panasonic proprietary interface), my schematic and few other parts.
The PCB will be pretty simple. One IC, one capacitor, a couple of connectors. At first I couldn't believe how anyone could make such a simple interface board for a CD-ROM and have it work but after taking the unit apart it all falls into place. It doesn't use an IDE CD-ROM drive! It uses a Panasonic (Matsushita) proprietary interface (MKE). The drive is a Panasonic (Matsushita) CR-563-B 2x unit. Some of you may even have one of these laying around because they shipped a lot of them with Creative Labs SB16 CD-ROM kits. There is also a CR-562 that is basically the same drive without the digital audio out on it.
The interface board I have also looks like it has an option to use a serial interface and possibly use a Sony proprietary interface instead of the Panasonic. The Sony parts aren't stuffed and I'm not going to bother trying to trace those out. My PCB will be Panasonic only.
Go to http://www.cadsoftusa.com/freeware.htm and download the freeware Eagle PCB program.
Get my cd7 schematic and preliminary board layout (you'll need to autoroute it).
I don't know if it's clear from the board layout but the db25 connector is installed from one side of the board and the CD-ROM header connector (and everything else on the board) is installed from the other side.
(My ISP is dropping me at the end of the month so grab the files now if you want them).