Since you have two physical disks, I just want to be sure how you created your C & D volumes. In Win7 volumes can be either be Basic or Dynamic types. In addition, Dynamic-type volumes can be either have Simple or Spanned layouts; whereas all Basic-type volumes can only be Simple.Typically, you want to use Dynamic-type volumes to create spanned disks to create a virtual bigger disk.In your case, there really shouldn't be any issues with installing FSX on the D volume. However, there are a few things to keep in mind: 1) If you ever want to change the Dynamic disk back to a Basic disk, you will lose all of the data on the disk unless you back it up first. 2) If you later add additional physical hard drives, you can extend still extend the D volume (if that is your requirement) without having to reformat it. Note that when you extend the volume over multiple disks it becomes a Spanned volume.