I cannot put into words why, but the thought came to me to disconnect the two external hdd's that I had connected and been using previous to attempting to solve the problem with my scanner in the XP Mode.
When I disconnected the two external hdd's, WinXP quickly recognized my scanner and installed the necessary drivers, all in about thirty seconds. Wow! That was a surprise.
Still, I have no idea why the connection of the two external hdd's in my host pc would prevent the installation of the scanner in my guest pc. But, needless to say the next time I need to scan I will make sure my external hdd's are not connected.
My thanks to all who responded.