ASUS P5K mobo software underclocks my CPU!

why is my P5K mobo software underclockign my e8400? the software monitors the cpu speed and it alternates my FSB mulitplier between 6 and 9 when using less intensive tasks, 6*334mhz or 9*334mhz. How do i stop this cuz it always happens. When playing crysis i pressed ctrl-alt-del and looked at it it says running at 3.1ghz then after a while 2.1 ghz if i overclock it with the p5k software. I've checked on CPU-Z and my CPU is being underclocked. How do i keep it at stock speeds 3.0ghz instead of 2.0ghz cuz my PC starts lagging after playing Crysis.
Specs:
E8400
ASUS P5K
Geforce 9800gx2
A-Data ddr2-800 2x2gb
Windows XP, Antec 900
This is off topic but the 9800gx2 is running at 50-60 degrees and 60-70 for the 2 cores when idle. Is that normal, when gaming the temperature goes up 10 degrees but the fan doesn't speed up its always at 45% speed.
Plz help

its called "SPEEDSTEP TECHNOLOGY" or "EIST" disable them then you are free!