Because of this problem, I moved my iTunes files from my Windows 2000 machine to my Windows XP laptop and updated to the latest version, just for the privilege of continuing to buy from Apple. Now I discover that I needn't have done so, and am contemplating whether to go to another whole load of bother to move my files back again to the machine where I really want to run iTunes. I have to say this episode has left a very bitter taste in my mouth. I really expected more from Apple. The least they can do now is issue an official statement explaining what happened and apologizing for the inconvenience (which for some people must be considerable).
Of course, there should have been an announcement soon after the problem appeared, to the effect that "normal service will be resumed as soon as possible". If had been made known in a more timely fashion that it would not necessary to upgrade, many people (I suspect) would have been saved a lot of hassle.