There are 4 computers in this home. I was using Windows XP Pro and the others Windows 2000 Pro. Since I do all of the service on them I decided to change my computer to Windows 2000 Pro. I immediatally noticed a reduction in frame rate in FS9, but I decided to live with it. About 2 weeks ago I procurred the Manhattan Scenery from Aerosoft, and noticed that I had a frame rate of about 8. Last weekend I changed back to Windows XP Pro, and when flying in Manhatten my frame rate was consistantly at or above 15. This convinces me that Windows XP is the way to go for FS9.