Need Halp!!!

Before I blow up my PC, I wanted to get some advice about cooling my CPU. Running an Intel E8400 DualCore in an Antec Sonata case. Was running the CPU with stock heatsink @ 55C (idle). The shit always beeped and got too hot when playing Source Engine games (Strangely enough, never when playing Crysis). So I bought thermal paste and applied and got maybe 2-3C better temps. Nutted up and bought Arctic Cooling Freezer 7 Pro and installed. Now the proc idles at about 46-47C but still overheats constantly. I've tried running the fan at full speed with no luck and I see forums where people talk of this same processor at 30C idle 45C when OC'd. How the fuck do these people get these temps? What am I fucking up?