I have an eVGA socket 939 motherboard and want to upgrade to a dual processor. There were limited choices at newegg, so I searched Frys.com. They list some AM2 socket processors under the socket 939 section. Are these two sockets interchangeable?

Socket 939 and AM2 aren't interchangable. It was probably just a mistake that one was listed with the other.

As far as getting one goes, it seems like 939 is being phased out. When I got my system a few months ago, there were as many 939 Athlon X2 processors as there were AM2. Now it's hard to find them. They're around, just in smaller quanities.

You'll need a socket 939 one, though. You can't use AM2. Make sure you can use an Athlon X2 at all. Your motherboard may not support it.

AM2 was launched last summer to replace 939. AMD hasn't been manufacturing 939 processor for quite a while.