Our problem looks fixed, so here is what happened. I hope it helps others.
BTW - I live in Fremont, California and am just here to share this and head onward to other pending stuff.
I installed Nero software to Win2000 Pro when adding a Memorex USB DVD recorder. It worked fine until I tried to upgrade Nero software, and lost visibility of D and E CD/DVD drives in Windows Explorer.
Troubleshooting device manager showed two drives working properly. Admin tools showed errors with file cdralw2k unable to load.
cdralw2k already existed in two forms on our machine, but I downloaded another cdralw2k driver file from driverguide.com. After renaming the existing file, I copied the new file to ...drivers\system32\drivers.
Still no drives showed after a reboot. So then I saved the new and renamed the BAK version to both filenames cdralw2k.sys and cdralw2k(with NO extension). All drives showed after another reboot.
There's 2 variables here, one that the BAK version was OK from the start but missing in its no-extension form, and one that the new version was not tried in its no-extension form. I don't care because it works now. I had already backed-up everything and was ready to reload the OS from scratch.
It looks like Nero just cleared off too much in its uninstall. What a time waste. Later.