Go for the Quadcore for sure, I have one and it's great.
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Intel QuadCore Q6600 2.4GHz - 4GB RAM 800mhz - Geforce 8800 GTS KO 512mb - Creative SB X-Fi - 2x 320HD - LCD 22' WS LG Monitor
Lowest score in windows vista: 5,6
Life can be so easy if you have a good video card ^_^