You have to make a certain number (3) of hardware changes, any installed hardware, within 90 days. Wait 120 days between upgrades and you can go through a lot of hardware before you get nailed with the dial up registration.
I had literally replaced everything in my system until I screwed up one XMAS. I changed the DVD in and out too many times trying to get the POS to work, that along with another upgrade I did triggered Windows.
Note Stripping out hardware and reinstalling it as part of trouble shooting can cause you to exceed the change count. So before starting trouble shooting save your final hardware key file.
WOW just read that link Gonaads. Best description and utilities I've ever seen on activation. REP points time.
Ooops. Almost screwed myself. Added a stick of RAM, changed the DVD at XMAS and for some reason it thinks my video card changed??? If I pull that stick of RAM out I'll be dialing MS again. Handy little utility XPinfo.