Hi newcomer and welcome to the Tom's hardware forum.
You PC currently is running at 667MHz, BUT, Why you only see 333MHz?.
Explanation: DDR means double data rate, the double means that you need multiply the speed that you see by 2. 333x2=666MHz, that is the 667MHz speed that you usually know.
With that explanation, your current mobo is running with a RAM 667MHz, so, is supported.