A couple are Sony DVDs, but not all that I've been trying. I wanted to use my camcorder for better quality and because it's easier to download to my computer.
I did some more experimenting and found a solution - use the camcorder as a pass through to the computer. I plugged the dvd player into the camcorder via RCA and S-video, then plugged the camera into my computer via DV/firewire and removed the tape from the camcorder. I then was able to capture the video (Adobe Premiere) to my hard drive without anymore "copy prohibit" messages.

problem solved - though it would still be nice to have the option of recording to tape in case a computer isn't around. Oh well.