There were a few caveats depending on manufacturer. You can read up on it. I believe one had to do with HP/Compac models with AMD processors. I've personally done over 50 upgrades from old laptops to newer rigs and have yet to have a hiccup. Download the full package and either burn to CD or run from a flash drive. Install it after a fresh reboot, with the AV program disabled and the no internet connection. If your system is otherwise sound, you're ok.
I know you're supposed to wait a while before installing a new service pack for Windows. Is it safe to install Service Pack 3 yet? I put this question to the "Wisdom of the Masses."
Raymond in Athens