Drill 2 3/4" holes into the sides of the newell about and inch or so from the bottom, (you can also go bigger to give you more room in the hole) make them about and inch deep or so. get yourself some 3/4" plugs (or make them from a dowel) then use some heavy duty 4" screws or lag screws and drill them into the holes at enough of an angle to go down deep into the floor, I would predrill a hole for these first. Make sure you set them deep enough and far enough back into the hole so the plug fits in..then glue and plug and sand and your golden..A newell is required to take 250LBS of outward pressure to pass building code. this method if done properly will get you there.
you can also buy a newel anchor like this one...very easy to install, helps plumb the post too by alternating the tightening of the screws..
http://buystairparts.reachlocal.net/Pro ... =72&cat=32