Thanx, Rene.
My Pismo's DVD/CD drive (in the expansion bay) reads most CDs just fine; it's only the occasional old data-CDs (received from my Wintel-using clients) which often fail to mount.
These same old CDs mount on my iMac, though. I am more than a little puzzled by this, and was hoping for some PC-Exchange or keyboard-command "fix" was available.
I appreciated your comments, and may have my DVD/CD drive looked at the local Mac repair shop.
Regards, T.