It's obvious you need to upgrade. Get a new motherboard and a new CPU to play Crysis:
Consider any of these CPUs--E6850, E6750, E6540, E6550 (all are Intel Core 2 Duo). The ultimate prize is the Q6600 Intel Core 2 Quad. Although a new revision of that is coming soon.
For the motherboard, just get the one I linked. Total cost should be around $250-$300. Conroe is defintely better than an Allendale but comes at a higher price. You get what you pay for. That's all I can say. Bottom line is just get the one that fits in your budget. If you want performance, you're going to pay high price. Otherwise, the Allendale is a steal.