On Mon, 27 Apr 2009 19:21:30 -0700, Jonathan Sachs
wrote:

I used to own a house that was built on a stemwall foundation. I
grounded the electric outlets by drilling a hole up through the bottom
plate under each outlet box, pushing ground wires up through the hole,
and fishing them into the box.

I'm now buying a house that is built on a slab, and many of the
outlets are ungrounded. How should I deal with the problem in this
case?

Your main has a ground. There are other ways, but you need to know
local codes.