I upgraded to BK 6 while still running my windows Vista and had no problems at all. At first I kept my BK 5 as well, because there were things I liked better about it, but in time, I found I had all that and more with BK 6. Three months ago I got a new computer with Windows 7- 64 bit. I expected problems changing from the 32 bit to 64 bit. It was one of the few programs on my computer that made the transition smoothly. Some of my Virus protections had more trouble in the transition then BK 6. I am very happy!!