I assume they all work (my two 512s and the two I just got from a spare computer) but I didn't check for certain that the ones from the spare were working. It was running fine, just had a CPU half the speed of mine.
Yes, this motherboard has 3 slots, DDR1, DDR2, and DDR3. I've always had one in the first two, and I just put one in the third one. I didn't see a 'remap' but I'll have to look. There's the DDR speed clocked[?] to the CPU, the DDR voltage setting, etc..