when there will be methods in SDK to set cpu frequency ?Also to set the voltage would be fine.
You can check out the power management tips from URLs below: http://www.intel.com/cd/ids/developer/asmo-na/eng/dc/centrino/power/index.htm
Currently, I am not aware of any SDK that can do what you are asking.
Here is another article that also related to this topic: CPU Power Utilization on Intel Architectures
One thing that you need to consider is that switching P states of the processor may cause system instability. Normally, it is best to let the operating system and system management software to handle the switching.