FAA Commercial Glider License Questions

All,
Thanks for all the useful information. I atually already have a
"restricted " FAA Private Power (SEP) and Glider license on the basis
of my UK gliding experience and my JAA PPL. I had never considered
that you might be able to upgrade to a commercial this way based just
on previous experience. I wonder if its possible to "upgrade" from
Private to commercial based on experience even though I already have
Private on my license?
As for training - thanks for all the suggestions. I will check the
websites and post back when I decide which part of the US to go.
Thanks again for all the info