Here is what he sent--
We were there in 1988. Nes (which means headland or promontory) is a common name in Norway, there may be a Nes in every county. Our Nes is in Hedmarken as you know. You can see it if you go to Google maps and find Hamar (north of Oslo) and then look to the west. At the tip of the peninsula into lake Mjsoa, you should find it. Petterborg is a place name; the name of a farm. The original settler (no relation) was named Petter and this was his borg (castle). Our name was taken from the site, not any person. The people that lived at the farm when we visited in 88 were named Stollen (the other name of the mailbox). If you look south from Nes, you will see an island, Helgoya, connected by a bridge. Our family lived on a farm at the southern tip of that island prior to moving to Petterborg.
The name should be pronounced Petter Borg, not Peter Berg the way I grew up.
I have received some aerial photos of the area from R.P. but I was waiting to post them until I have a source. They are a great view of the area. Look for a post in the near future.