If you are going to eventually purchase a professional license, along with an FAA-certifiable simulator, you might as well spend $100 on a basic yoke:
from here:
http://www.mypilotstore.com/MyPilotStore/secp/68
or this one:
http://www.mypilotstore.com/MyPilotStore/sep/4127
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Even then, a yoke or joystick is not a sheer requirement. X-Plane 10 can be used with a mouse alone. However, it can be difficult to control the aircraft with only a must, and it may not necessarily accurately give the proper impression of the feel of X-Plane.
If you are just hoping to test X-Plane 10 to see if you will like it, download the Demo first:
http://www.x-plane.com/desktop/try-it/ (scroll down).
If you like the Demo, you can go ahead and buy the "Global" version to see the scenery on a full scale. Keep in mind that X-Plane 11 is coming out within the next two months, but considering X-Plane 10 has already been approved, you may want to stick with it for now.
If you like what is in "Global", then you can go ahead and purchase that certifiable license. If you want to effectively project X-Plane and use it in a professional simulator, you must purchase the license here:
http://www.x-plane.com/pro/
The professional license allows unlimited flight and licenses the simulator. It also allows for wide-angle projection or spherical projection of the simulator. On top of this, you can drive real Garmin units with the professional version.
* The X-Plane Global CDs must also be used to install scenery into the professional version.
I know I went off on a tangent. :) Yes, X-Plane can be used with a mouse only, but I wouldn't recommend doing flights with it.
(see comment below) --v