Sensing position in 3D or 2D space

I'm thinking of doing a project that involves sensing the location of someone's hand, so a robot can shoot a ball towards that location or something along those lines. My problem is I have no idea where to begin with sensing the location.

I was thinking I could... 1. use one or more accelerometers to determine how much something has moved around, but I'm against this idea because it would mean somehow sending wireless information to the robot, or what ever device I'm controlling, which would get a little bit complex. 2. use an infrared sensor or camera and an IR LED so I could track the location of the light. The problem with this is that I don't know of any cameras or other sensors that could do this, and return simple information that I could use (such as location of the light on an x/y plane etc).

Any suggestions would be helpful. ;) Thanks.

The Pixy camera can follow colored objects, and report positions in 2D http://charmedlabs.com/default/?page_id=211

Thank you remington, I'll check it out :)

Friends of mine are using the Kinect to sense position and distance.