I have newly installed electric radiant in my LR, very happy with it,
as it heats the LR without cooking the 2nd floor BR. Seems cheaper to
run than the furnace as well. Needs insulation below it for good
efficiency. Can you add another 2" height to your proposed floor for
the insulation? Otherwise, the slab sucks btus downward. Mine produces
30btus/sq ft., enough to warm the room 10 degrees in about 45 minutes.
Here are some links I came across while researching this:
http://tinyurl.com/4znaz
http://www.heatinghelp.com/
http://www.taunton.com/finehomebuild...ges/h00028.asp
http://www.pexconnection.com/
http://www.radiantec.com/
http://www.rpa-info.com/forums/Ultimate.cgi

That ought to get you started. I was at first going to use water, but
my contractor pointed out that electric is pretty much zero
maintenance, whereas water systems need to be regularly flushed and
maintained. Also, if you're in an area of the contry that freezes,
special mixtures must be used. My system is from he
http://www.heatizon.com/

Good luck, let us know how it works out.