You really need to get an after market fan. You won't get very far with the stock fan to see much improvement.
If money is tight, then the Cooler Master Hyper 212+ is an excellent purchase at $30. I use it on my X3 which I've overclocked to 3.61 ghz (x18) and I've also unlocked the 4th core. This required me raising my CPU voltage to 1.5, but my temps stay around 33c idle and 47c full load.