Like he said, nope. The Athlon64 design incorporates the memory controller onto the CPU die itself rather than the chipset on the motherboard. (This is primarily where the A64 get's it's performance from.) The AM2 chips work with DDR2, while 939 ones work with DDR. DDR1 and DDR2 are not cross-compatible with each other for starters. And like LoneStar mentioned, the pin-out's are different for AM2 chips with voltage and data pins, not to mention the keyed parts of the AM2 socket. You couldn't put a 939 CPU in an AM2 socket without damaging the CPU.
