I swapped out the IDE cable and took out the two sound cards-- problem remains. Was about to consider buying a new mobo when I thought to myself, "why not try yet another cd drive?" And sure enough, I try it with a THIRD cd drive, and it works. Who knows, maybe both of the other two drives are screwy, maybe not, I think I'm going to just chuck them both out regardless.
Thanks again for all the help.
-Andrew