yes, socket 940 are for Opterons (server CPU's), and the FX-51's and FX-53's
socket 939 can hold a 3000+, 3200+, 3500+, 3800+, FX-53 or FX-55 chip
socket 754 holds the Sempron 3100+, Athlon 64 2800+, 3000+, 3200+ and 3400+
note there is a difference between the socket 940 FX-53 and socket 939 FX-53
I reccomend if you have the money, to go with socket 939, but socket 754 is still pretty good