Toasty7....proper airflow is very important...especially when o/c'ing. The generally accepted way is to have a front fan, usually down low in front, pulling air into the case...a rear fan pulling air out of the case....the cpu fan ( if there is one...),blowing towards the rear fan. This creates a good airflow from front to rear. There are also side fans that blow towards the cpu...top fans that pull air out of the top of the case...and then the psu fan (fans) also help some...oh...almost forgot about the graphics card fan ( if there is one).
I have the AC Freezer 64 Pro...120mm fan in front & rear...my psu has two fans...fanless graphics card ( I'm not a gamer...but have a good card with 256Mb. onboard memory).
I have an Athlon 64 3000+ s754 Venice core o/c'ed from 2000Mhz stock to 2640 Mhz stable...idle temps are about 35 deg. C....and no more than 50 deg C. running Prime....
I like the Freezer 64 Pro....very easy to install on my AMD system....didn't have to remove board...snapped in just like the stock one...even with the fan speed turned down with my fan controller it cools great...maybe 1 degree difference...and very quiet at lower speeds....not near as heavy as the Typhoons, Thermaltakes...etc....