I have a very good setup of 31 idol for my 2500+ OC'd to 3200+. 2 Fans comming in over my front to my hard drives and side panel going in and 2 rear going out. Think about how the air flows..
Hard drive cooler on my SATA.
Two fans in front case blowing to the rear of PC.
Two rear exhaust fans underneath power suppy.
Two exhaust blowers occupying the PCI-e or PCI slots.
One side fan blowing in (I believe this helps the CPU a lot).
Of course, a fan on the CPU and motherboard chipset.
Power supply comes with it's own fan.
So I have like a total of 5 fans blowing out while the other fans are blowing in.
the fan on the heatsink is supposed to be blowing out....the heatsink draws the heat away from the processor, then the fan pulls the heat off the heatsink...blowing out...duh
Your CPU fan typically will be blowing air towards the heatsink unless stated otherwise (for example Alpha Heatsink/Fan combos are meant to pull air from the bottom of the heatsink, away from the CPU).
You can experiment with that if you wish. It's very easy to do. I have mine blowing in and I'm using a 3500+ 64-bit CPU. CPU runs idle like at 29 some odd degrees C. That is cool.