You have one little issue.... AM3 motherboards don't support AM2+ CPU's. You can purchase an AM2+ motherboard that supports an AM3 CPU but not the other way around.
I would go with MSI 785GTM-E45 AM3/AM2+/AM2 AMD 785G
or ASUS M4A785-M AM3/AM2+/AM2 AMD 785G
Nice recommendation ... will it support my RAM BTW ?