The only experience I've had with activation is on XP. I did a re-format and had to call MS to activate the serial number. I just told them what I did, my serial number, and that it was on the same Compaq computer and they were fine with it. I was actually a bit surprised how easy it went down. I was expecting Bill Gates to Blue Screen of Death the screen on my phone, or the laughing skull and crossbones from Independence Day to show up.