This is assuming your case has good airflow and you dont have a fan already. I have a fan and get 60°c all the time so this dosent help at all.
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Q6600 Core 2 Quad || Soundblaster X-Fi Extreme HD || e-VGA 8800GTX || 4096mb 4-4-4-12-2T Dual-Channel RAM || MSI P6N Diamond || 2x 320GB Hardrive || 5.1 Speakers || Remote control || 8x USB 2.0 || DVD/CD ±RW Drive || 1x IEEE1394