See
http://www.thinkgeek.com/computing/input/keyboards/5e2b/
http://www.halfkeyboard.com/
Cool.
I think a person could take an off-the-shelf full QWERTY keyboard
and chop off half the keys (following the directions at
http://www.trevorblackwell.com/keyboardchop.html).
As far as I can tell, the result would be practically identical to the above half-keyboards.
Then, is the software from
http://half-qwerty.com/
all you need to use this hacked-up half keyboard?
http://www.almaden.ibm.com/cs/user/inddes/halfkb.html