I don't know how much of an issue price is for you, but I wouldn't worry about the processor too much, get any C2D and if you overclock it properly, you'll be set for quite a while, I mean, I've seen the X-bit labs people overclock an E2160 to 3.4GHz (a little hard to get to, but achievable) and it beat out a stock X6800 in their benches that included various applications and games. I wouldn't worry so much about getting a Quad core yet because I really doubt that games within 2-4 years will even take 100% advantage of a quad core. Plenty of people are still able to play modern games on single-core/good-graphics card setups. Games are much more GPU-intensive than they are CPU-intensive. Heck, I remember being able to run FEAR, Doom 3 and HL2 on my 1.6GHz P4 which ran on 512MB of PC100 memory, and thanks to my 9600XT, I got about 40-50FPS on low-med settings (maxed out in HL2) and 30FPS in really intense parts. I got that computer 8 years ago (the video card I upgraded in late 2003)
But of course, if you've got the money and you're very comfortable spending it, then go right ahead and keep yourself future-proofed.