When you overclock your RAM, you actually are overclocking the FSB of you CPU. Because your RAM is directly connected to your FSB, the RAM overclocks as well.
You have noticed RAM that is higher than PC3200. If you were to take that faster RAM and put it into an unoverclocked system, it would just run at PC3200 (which an unoverclocked CPU defaults its RAM to).
Have a look at the stickies at the top of the Overclocking forum. There is a really good chance that all of your OCing questions will be answered from those.
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