CPU throttling

I've got a 3.5 inch SBC running a Cyrix Geode (PII class) processor at 300Mhz. There is a CPU throttling option in the BIOS that goes from 12.5% up to 75%. It's actually a duty cycle method, not true throttling. My question is, are there any programs available that would allow me to change the duty cycle within Windows (or some other OS whether it be *nix or FreeDOS), and if so would I be able to set the proc to 100% as I plan to add active cooling anyhow and there is only passive at the moment. I'm going to put a chipset sized fan on top of the CPU sink.