or google it
dont buy one
I got one and its rubbish
I work at an animation studio here, and we have a 3D character that is activated by Motion Sensing as you describe there.
But it takes like 15 minutes for them to calibrate all the points, with an $80,000 piece of machinary. But the only thing with that is, the model person has to wear a full suit with sensors everywhere (and when I say everywhere, I mean... EV-ER-EE-WHERE *shudders*), with the Wii you could get away with probably 4 wiimotes. Two straps on your arms and two for your legs, velcro straps, then fasten the Wii motes in.
Much like that idea with the Wii-Glove for boxing games... Hrm.
STOP STEALING MY IDEAS! :P just kidding. It's a common thing that a lot of people want i think but i did just put this in my 8th generation console thread. I'd say that nintendo will make something like this for their next system.
System not console.
'Boards don't fight back' - Bruce Lee
Money spend on Wii:
$50 Pre-ordered Wii console
$10 Pre-ordered Legend of Zelda: Twilight Princess
$100 Xbox console trade in
$339.95 extra paid off
$499.95 Total I'VE PAID IT OFF!
I don't think they would actually. The approach they had for the Wii (I know you said "system not console") was so that you could either be immersed in your game, OR simply pick up the Wii-mote and have a short burst of fun... a Woody-Allen-in-the-sack if you will (very short burst probably O_o).
The idea of them making a full-body motion sensor controller will probably seem too immersive, and that's the sort of thing they kept away from this gen, one of the reasons why the Wii is becomming so gob-smackingly anticipated.