To the above poster: Dynamic frequency scaling has been a feature of intel processors for years, it's not unique to Nahalem.
To the origional poster: CoolBook isn't for under-clocking, its for undervolting. There is a big difference, your processor speed is unaffected when you undervolt your CPU. When you undervolt, you are tweaking/optimizing how much power is used (and thus heat generated) for different frequencies.