I read an article about dual core processors being good for gaming and the extra cores not really mattering. I guess that guy was wrong?
It depends on how the game was written. If the game itself was written to only use one core, then dual core usually isn't going to do much for you. Just because a CPU has more than one core does not mean that every program will take advantage of it.
GTA IV was written to take advantage of multiple cores. Specifically, at least 3, best 4. In order for a program to take advantage of multiple cores, it must be written as such. So, most games were written for single-core systems. Hence, the extra core usually does NOT translate into better performance on a multi-core system.
So, the author is correct in a sense, depending on the game. In the case of GTA IV, it DOES pay to have more than 2 cores. I can definitely attest to that.
I had an AMD Athlon64 X2 4200+. The game ran like crap. I was lucky to get 24 fps if that.
I upgraded my machine to an AMD Phenom II X3 720 BE. With the same GPU from the X2 days, the game was MUCH more playable. I've since unlocked the 4th core (which hasn't seem to help GTA IV much), but I went from around 14 fps to an an average of around 35. I since upgraded my video card and I now average around 40 to 45 fps.
So, depending on the game, multi-cores may or may not have an affect on their performance. However, newer games are being written to take multi-core processors into account, so more and more games WILL be affected by it.