I installed on my Mac Pro in Bootcamp Windows Vista Ultimate, activated it, works fine. I then installed in OS X Parallels Desktop 3.0 and created a virtual machine that started windows vista in bootcamp. Activated with the same windows vista activation key windows vista in Parallels, everything worked fine. Problem: A few weeks later, when I started windows on the virtual machine in paralells, windows complains that it is has to be re-activated (strange,as it was activated before). So I tried to activate it again, but it complains that the serial number is already in use. If I boot windows in bootcamp and check the windows activation status there, it says "genuine activated version". It seems that somehow it now refuses the same serial number for the virtual machine in parallels and wants me to buy a second serial code. Does anyone know a solution to this? I do not want to buy a second license from Bill Gates. Thanks for sharing your knowledge with me!