Speedpig is based on the same idea as another piece of software (commercial) called SpeederXP which can be seen on the link below
http://www.speederxp.com/en/
and in the details it says it changes the speed of the cpu, which would be the FSB (i dont think Multipliers can be changed by software).
If your pc doesnt support any means of fsb changing (which is highly unlikely) then any speed increase you feel is purely psychological