yeah, aren't AM2 socket CPU's the same as s939 but with ddr2 memory.
They are actually going to be socket 940 with different pin outs than current socket 940. So current socket 940 cpus wont work with new AM2 socket 940.
They are simmiliar to socket 939 in the sense they will use the same cpus. The new AM2 socket 940 will still use Athlon 64 cpus, but just AM2 versions of them that support DDR2.
This upgrade is kind of like when AMD went from socket 754 to socket 939. They still used the same cpus, but different versions of them that supported the new socket and DDR dual channel.