NVIDIA nTune can automatically optimize your system by running different analyses on the system components to test their performance, or you can use it to manually configure your own parameters.
The main changes that you can enact with NVIDIA nTune are processor speed (overclocking), voltage, and fan speed.
It's also possible to configure dynamic access to BIOS, but only in those motherboards that include that ability. In any case, be careful with what you do, because an error may leave your computer unusable.
The only operating system that NVIDIA nTune supports is Windows XP.