I'm not the skuzzmeister, but...
pc3200 is a nice match for current socket 939 boards but AMD would be crazy to stick with a 200mhz fsb. Intel has already pushed their officially supported bus speed to 233mhz, and many overclockers are proving that 250mhz is not unreachable even with current hardware. Based on that, I'd expect the standard FSB to jump to 250mhz eventually and pc3200 will be a bit slow. If you're going to want to use it in a future computer, you will be better off with pc4000 or getting very high quality low latency pc3200.
If you can find a great bargain on pc3200, then that might be a reason to get it because most computers will let you run the memory at a slower speed than the cpu's FSB, but you'll see a performance hit.
I wouldn't buy more stuff now to put into a future computer. Buy to fill your needs now, using as high a quality of parts as you can afford. Then when it's time to make a big upgrade, you can reuse those parts that still make sense to reuse, but you're not tied to using expensive but obsolete parts that you'd purchased long before simply because you wanted them for your next computer. Fill your needs now, and if you choose wisely then some of those parts will still be usable after future upgrades. PC4000 is pretty much the top of the line spec for DDR, so that would probably be the safest way to go. Just look at the rated timings at that speed to figure out how good the memory is.
Or get the cheapest (but still name brand) memory you can right now, and give up on the idea of moving it to your next computer. Fill your needs now with what goes good in your current system, otherwise you're chasing the upgrade train and you'll never catch it.
