I'm happy to report:
Transferring the i-Tunes music files via drag-drop right into the external hard drive...WORKED.
I was able to send a couple of Alicia Keyes albums (one was downloaded from my music CD; the other was an i-Tunes electronic purchase) to the thumb drive; then right on into the old XP computer; then right into the new i-Tunes!
I'm listening to Alicia (on the XP laptop) as I'm typing these words from my VISTA laptop.
All's well that ends well.
Thanks for all of your help, EVERYONE!