M$ claims that you have to change 6 components (hard drive, amount of RAM, etc.) to force a new registration. Independent magazines have said they've had to re-register with just 3 upgrades. You can do electronic registration instead of calling in. The serial is something obnoxious like 50 characters long. I'm using XP without much issue, but I've also loaded things like firewall software and XPAntiSpy to keep XP from "leaking" stuff out. I deliberately disabled the Windows AutoUpdate, but it kept trying to update me anyway. Between my firewall software and XPAntiSpy, I haven't heard a peep from XP in a while. Beware Windows Media Player 7 which has tracking software and a Unique ID number, which M$ would never use ...