I did a thread search for this same topic and could not find it:
Are there any software issues (i.e. "bugs") with loading FS9 and FSX on the same computer? Obviously I won't be running them at the same time...I just didn't know if it would cause my computer to crash or mess up settings/addons between the two in the event there are duplicate files and my computer can't tell the difference. I just recently bought a new computer and the hardware I have (RAM, Video card, etc) are more than sufficient to run FSX. Any insight/comments are appreciated. Thanks!