try to get the 78-S2P board, it has support for AM3+ processors(future-proof) via a BIOS update.
78-S2 doesnt have that, though it supports AM3 completely
Avoid 68-S2P, becoz of this:
* If you install AMD AM3 CPU on this motherboard, the system bus speed will downgrade from HT3.0 (5200MT/s) to HT1.0 (2000 MT/s) spec; however, the frequency of AM3 CPU will not be impacted. Please refer "CPU Support List" for more information.
So choice pref shud be
Gigabyte GA-MA74GMT-S2 (this one is based on older chipset, but has full AM3 support)