Pretty sure socket 754 is 64-bit since they began, but they can handle 32-bit processors as well. I am currently looking at purchasing a new board that is 754 with a AMD Athlon 64 3200 myself.
Do you have a specific board already? If you are going to buy one, my guess it that it will support it.
I am a computer reseller and yes, you can use almost any s754 motherboard, from the cheapier (MSI K8MM with IGP) to the MSI NEO 3 (nforce 3).
I manufactured a lot of Sempron64 computer and they all works like a charm