For gaming:
Single core:
Amd 64 3000>Intel 3-3.4 or higher
Dual core:
X2 3800 > Intel D930 or maybe even D940 and for gaming better than maybe even D950.
Get Amd X2 3800, simple, amd does more clock cycles per second.
AS for single core, get amd 64 3000-3500 + good mobo + good cooling+ better ram and most importanty best graphic card. Just OC the CPU.
or get x2 3800 around 8k or so