Underclock

I've seen many people using that so called Underclock on their PC's.

I was wondering...how can I underclock my PC without accessing to the BIOS?
I'd like to underclock it too because I play in servers where people got so extremely high pings.

Which software that actually works properly should I use to Underclock my pc and play Gunz as the underclockers do?

Thanks beforehand.

use net limiter remember to thank me if it helped