The AMD Athlon 64 3200+, then overclock it to 2.4ghz and you will really start to see a preformance increase over the Pentium 4 640 3.2ghz processor in terms of gaming.
Although Intel processors a good processors, they are overrated for their price IMO.
Pemtium D Smithfield cores are a prime example of that. Worst dual core processor you can buy. Infact they are that bad of a dual core processor that a single core mainstream processor can out benchmark them in nearly 90% of all benchmark test when up against the same ghz speed. Xbit labs had a big artical on the first generation Pentium D's
