The free utilities such as Rain only executes HLT commands, which is usefull in win9X environments. NT OSes (winXP) already have this function built in. Utilities which offer more functionality, such as CPUIDLE (which includes chipset specific enhancements) cost money, so you are out of luck. On a side note, you can check your bios for such features. Mine has a "CPU bus disconnect" option.... which is one of the things CPUIDLE does. It disconnects the CPU from the bus when inactive to keep the CPU cool. Keep in mind that all these solutions only work when the CPU is idle. When the CPU is running at 100%, no software cooler will cool it down. Nothing beats a good heatsink and fan.