Updating ati graphics card
They are usually used to increase clock rates but they can also be used to decrease them.A video card has two clocks which you can underclock: the GPU clock, and the video RAM clock.GPUs can usually be underclocked as much as you want but there's not much point in going beyond cutting the clock rate in half.Video RAM often has problems when underclocked by too much.The programs usually modify the actual clock rate which is, in this case, 200 MHz.
Increasing the clock rate heats the chips up which slows them down.
If your video card has DDR memory, then the clock rate which appears in the overclocking program may be half of what you expect.
It is common for 200 MHz DDR memory to be refered to as 400 MHz but that's not technically correct.
You should reduce each of the clock rates individually to see if underclocking solves your problem.
If that doesn't work then try reducing both of them at the same time.