Well here is my 2 cents.......I have Vista on this machine. Runs ok there are a number of things I do not like about it, but there are a number of things I do. If you are even thinking about DX10 Vista is your only option as DX10 will not be coming out for XP. That said, if you are running FS9 and do not plan on switching to 10 right away then Vista is not needed. There are still some compatibility issues with Vista that they will get ironed out eventually. The thing that drives me the most nuts is the security that is built into Vista.. Gotta click too many allow boxes... Yes just like the commercial! I have FS9 working on Vista but I am not ready to switch my sim over..... Just too early to tell if it will be worth the trouble just yet.