Is most overclocking done strictly at the BIOS level, or is there a way to do it from a running operating system? And if so, is there a way to do it from Linux? I'm running Ubuntu presently and am interested in overclocking to squeeze more speed out of my processor.
On the GPU side, there's NVClock and the nvidia-settings GUI, both of which support overclocking Nvidia cards.
As far as CPU overclocking goes, there's not much going for this on Linux, and you'll probably end up in the BIOS settings. Things are very different on Windows, where many motherboard manufacturers ship drivers and utilities for overclocking from a GUI without booting to the BIOS settings.
Underclocking, on the other hand...