I installed NIS2010 over NIS2009 on my wife's XP3 system. Part I was slick and lovely. It found NIS2009, uninstalled it and installed NIS2010. But not really. What it did was have everything in place for a reboot at which time the swap would take place, thus giving virtually no window of opportunity for malware to slip in between uninstall and install. Bravo for that!
But, after the return to the desktop, nothing happened. And then more nothing happened. And then still more nothing happened. Were it not for my experience with recent Norton installations, I might have clicked on something and created a disaster. Instead I waited. After almost five minutes (five minutes!), the activation screen popped open, I clicked okay, and the activation was completed.
Old settings were transferred over without problems and everything seems okay.
But remember, after the reboot, wait! And wait and wait and wait. Don't open other applications, especially not a browser, because any of these actions will try to invoke the security suite and the security suite is busy finalizing its installation. So wait.