Hagar it doesn't matter if you install fsx in the default location. It will ask for permission every time you try to do something but that can be easily fixed.
Right click on the folder that fsx is in and click properties & un-tick the box read-only & press Apply. Now it won't ask for permission when you try to install repaints & planes.
OK, thanks Andy. As I pointed out, I haven't got Vista or Win7. I'm only repeating what I've read many times on this & other forums over the years.
It might not be necessary but some respected developers recommend installing FS9 & FSX to the locations I suggested. It shortens the paths & should make them more efficient. It certainly won't do any harm.