Living in the Tampa Bay area of Florida we're at a high risk to have our computers hit with surges from lighting. Unfortunately, this happened to my daughters computer and I was given the task of replacing the MB and processor. The MB was a Biostar T-Force 6100 939 and was replaced with a Biostar GeForce 6100 M9 just like I have in my main copmputer. The processor was a AMD Athlon 64 3000 Socket 939 and was replaced with an AMD Athlon 64 3200 939 I had laying around. Both items are similar but different. I have 2 new unopened OEM Vista Business copies I received from MS via their express upgrade program and intended to use one of them on this repair build. After plugging in the new machine, and starting the boot sequence, I left my workbench to go get one of these OEM Vista disks to load. When I returned I was amazed to see that the original OEM XP OS had booted and was presented with the desktop. HOW COULD BOTH MB AND PROCESSOR BE CHANGED and not require re-activation????? I was astonished. I logged on and went directly to Windows Update site where my system passed WGA with flying colors and updated as if nothing had changed. Granted, the MB and processor are very similar but they are different. Go figure. Looks like I can keep my Vista disks for the next catastrophe.