Actually, that's precisely the point. If the OP is playing games from the last century, he probably doesn't need today's hardware to run it well. To say that a quad core would be beneficial to him just b/c he watches a movie on one monitor and surfs the web on another, or downloads stuff in the background while playing his old video games, well, all I can do is ask you how long it's been since you've used a single core CPU, b/c even that stuff could be handled with one. After all, it's not the most demanding multitasking scenario you've ever come across, and yet, with just the very hint of the idea of multitasking, you recommend a quad core CPU. That's knee jerk reaction, or thinking zebras when you hear hoof beats. Granted, you chose an "economical" quad core, and given the OP's current computer, it would make sense as a real, tangible upgrade, but at the same time, we both know the OP's current computer is more than up to the tasks at hand. Upgrading/building new would only be for the sake of wanting new, hardly not NEEDING new. And as we both can probably agree on that, now you might be able to understand why I criticize your recommendations. It's not a personal attack at you, it's a call against your judgment. The OP's original question was "SHOULD I upgrade my computer?" I'm aware that in your later posts you told the OP exactly the same thing I'm saying to you now, but the facts are the OP told you straight up in the first post his current computer specs, and exactly the things he plans to do/is doing on his computer. From that point forward, no one need mention a quad core computer, or 4 GB ram, and that's why I dinged your comments.
Now, sure, in the future (either near or far) the OP may decide he wants to play more modern games, or run more intensive applications. I'm from the camp where one upgrades only when there is the need. If in the future his hardware no longer suits him, he should upgrade at that time. It seems silly to build a computer for possible future needs when, at some point that future should come along, the computing technology available at that time would be undoubtedly better than the technology purchasable today. Building today for tomorrow is just a way to guarantee the computer will be obsolete tomorrow. For example, those poor souls who bought into 64 bit hype and purchased expensive Athlon64s on 754, only to have to wait 4 more years before a 64 bit OS (with drivers!) to utilize that trumpeted feature. I don't have to explain how "great" an Athlon 64 2800 runs Vista 64, as I'm sure you get the picture.
Now, OP if you just want to upgrade for the sake of upgrading, then just call it like it is. You can spend your money any way you see fit, but if you're seriously asking "should I upgrade", well then the answer is no, you shouldn't.
Joe