you can find these or similar devices to use to extend the box to the wall surface.......

http://www.aifittings.com/m_9.htm

"...measure once.....cut twice....throw that one away and cut a new one...."

While box extenders will work, that is exactly what they are made for, but let me suggest an alternate.

That is to skim coat the dry wall. First coat it with a product designed to lock in the loose fibers from the torn paper. IIRC it is called Guardz. A good paint store will have something for that purpose, but I think that I have seen it at the big box stores.

If you have any holes you will want to patch them with first and use tape where needed.

Then go over the wall with a skim coat of light weight joint compount.

I have skim coat fixed a number of walls. And while I have never installed new DW over old I have had to fix such walls where they burried the receptacles.

Also if you install new DW over old then you either will burry the trim and have to a lot of carefull cutting around the trim or remove all of the trim and reinstall with jam extenders.

You may find it easier to use 1/4" drywall instead of 3/8". This may eliminate the need to adjust trim as Bill points out. You will still need the box extender Doug refers you to.

Guys,

Thanks for the help. I have already picked up the drywall - will 3/8 still work? This is just one wall with no doors, so the only trim to worry about is baseboard. Thanks for the help with the box extenders!

farmboy