Your system MB has the 945P chipset. The 945P does not support C2D processors with a few exceptions. A few MB Mfg's including ASUS released 'revision 2' 945P MB's with revised proper voltage regulators to support C2D processors. Sorry, the DELL 945P MB will not support C2D. Certainly not the 45nm 7200. The latest Intel chipsets to support 45nm are X48/X38/P45.