The C-States program and idea kind of died but it has been replaced with a program called ThrottleStop.
There is a significant problem on many Dell laptops where Clock Modulation is used to slow down the CPU internally without warning users about what's going on. Some laptops also throttle back the CPU multiplier which can also significantly reduce performance.
This new tool can fix both of those issues plus it has the ability to set half multipliers on 45nm Core 2 CPUs, enable Super Low Frequency Mode (SLFM) as well as adjust voltage ID on the fly. At full load, only lower VID one step at a time or you might lose stability. It's a good idea to run Prime95 Small FFTs or similar when playing with this setting. On a T7200 I was able to lower the core temperature by 20C while running Prime by simply adjusting VID lower.
If this simple program dramatically improves the performance of your laptop then consider donating $5 bucks to encourage future development. This version will expire in a couple of weeks so I hope I don't have to add some nagging messages to the next release of ThrottleStop. I hate them.
ThrottleStop presently supports Core 2 and Core i7 mobile CPUs.