I have a T7200 2.0ghz, running Vista Home Premium. I have never seem that, but I never watch for it. It does sound like your power settings are wrong.
If you open a power plan, I would suggest High Performance, or create a custom one, and click change advanced options.
Under Processor Power Management > Minimum processor state set the Battery and Plugged in values to 100%. Then confirm the Maximum processor state is also 100%.
Make sure that is the active plan, and then check your speed.
EDIT: You could also try Updating your Windows Experience Score.
EDIT: What processor(s) are listed in Device Manager?
