I've had a look at the user manual for your motherboard and I can't see anything that shows how to set the memory bus to different speeds So :-
Why do you think the RAM is only running at 200MHz - is it a message, if so, what is the excat message that you see.
My supposition at this point is that the memory is running at 400MHz - though it's clock will necessarily be reunning at half of that.
You could try running Everest click here hich will tell you all about your RAM and speeds. If it's any consolartion, it shows my PC2700 RAM (333MHz) running at 166MHZ - which is down precisely to the Doubling effect of DDR RAM that I've been banging on about.