All three of those will work in an AM2+ socket, the 945 will be the strongest of the bunch, but the 925 and 620 provide more budget concious options if you are tight on cash. There is minimal difference between a PII and an Athlon II at the same clock speed. so the 630 is likely a better choice than the 925.
I didn't know you could use an am3 cpu in am2+ socket, I thought there would be an compatibility issue. with most of these cpu's is there any additional jumper settings or bios tweaks I need to know about after physical installation?
I just put an Athlon II X4 620 (AM3 CPU) in a Giga-Byte GA-MA78GM-S2H (AM2+ board, BIOS updated to most recent) and it works like a charm - well apart from having to manually set the CPU multiplier because it defaulted to 4 rather than 13....