THANK YOU VERY MUCH!
That was dead on. I did some checking between the good and bad files (on the XP machine) and lo-and-behold, the permissions were not the same. First I tried adding "Users" but got the same result. Then I tried adding "Everyone" and... bingo it works
I can only get to those security settings with XP "Simple File Sharing" checked OFF(i.e. Windows Explorer > Tools > Folder Options > View tab > bottom of list).
Now I want to know how to set the permissions for the rest of my files on the XP machine. The folder settings would have me believe that "Everyone" and "Users" were given full control. But that didn't happen. There's an Advance Settings box which seems to have some interesting options. Unfortunately I'm a bit confused about it right now.
Folder Settings for "Users"...
Folder Settings for "Everyone"...
The Advanced settings dialog...
Any tips on how I might straighten out my file permissions?