This site is being deprecated.
Please see the official X‑Plane Support page for help.
Here are our recommended computer specs for X-Plane 10. You can also try the free demo and see if it works ok for you on your computer. It has limited scenery and only 15 minutes of time, but other than that it's exactly the same as the default sim. You can even try your planes in it.
You can keep as many versions of X-Plane installed as you have room for. You would only encounter a problem if you tried to run more than one of them at a time. Just make sure the folders are labeled well so you know which is which. ;)
This site is no longer being actively maintained.