"Overclocking" your RAM simply means that you're running the system bus (FSB) faster than the memory is rated for. Since your memory is rated for 250MHz FSB (PC4000 or DDR500), you really aren't overclocking your RAM until you go past that speed. I doubt your new A64 will allow you to go even that high, so you really can't overclock your RAM in that system.
By looking at your posts, I think you have a basic misunderstanding of RAM and what it means to overclock it. RAM doesn't have it's own speed -- it has a speed rating. The motherboard settings determine the speed of the system. The RAM will either run at that speed or it won't. It's "speed" is entirely dependent on what the motherboard is set to run at.
The interesting thing here is that there are no "officially supported" motherboard chipsets that even support anything higher than 200MHz FSB. So, if you run your system above 200MHz FSB, you are overclocking your A64 and your chipset, i.e. running them higher than specified by the manufacturer.