The fix was accomplished by installing XP SP1.
Now I still don't know what could have caused it. Note that there was no hardware change since it first worked, but countless software installations and uninstallations.
So I am guessing that there must have been software confict that prevented WinXP from browsing the CD contents thru explorer (even though I could thru a dos window and 'safe mode').
Prior to SP1 installation, I had Nero 5.xx, CDRWin 4.x, and CloneCD. All seem to work fine together until recently. I then removed all the CD recording software that I could find, ran regclean and PC Cleaner (removes orphaned dll etc), rebooted, and it still could not read contents.
After installing SP1, browsing the CD contents worked.
The assumption here is that SP1 overwrote (updated) a file that was somehow in a conflict, currupt or not there.
I would still like to know what happened. So if anyone is familiar with this, could you please let me know?
Thanks in advance.
PS. Y'know, this is speculation but it seems possible that one of my games/applications may have updated software in an effort to enhance 'anti-piracy'. I found it odd that a couple of the games I installed wanted me to reboot my machine even though I declined the 'directx update' it wanted to install.