If you want to do everything as fast as possible, the dual core chills WILL be the way to go. Will? Yes. For now, not too many programs really use the dual core possibilities well. As these chips are quite expensive, you might want to think again wether or not go dual core. Of course, the future is dual core. So if you want to spend somewhat more money and have a system that will last somewhat longer, a dual core chip is a good way to go.
Anyhow… for your application, both AMD and Intel CPUs would work fine. AMD CPUs are as rock solid as the Intel ones. As long as you get a good mainboard with a decent chipset, you will be just fine. As the current AMD CPUs beat the Intel’s current models at about anything (including price), I wouldn’t recommend going for Intel. It’s like spending more money for less and there’s little point in that.
For what the mainboard is concerned… if you are aren’t into anything special like overclocking or tweaking every setting to the last bit, I think that most mainboards will suit you. Personally I’d stick with either NVidia or Via chipset based boards. From what I read in reviews, for most people, Ati and the modern SiS chipsets are good to. I didn’t try any Ati based board myself yet so I really can’t judge that well. For what SiS is concerned… I wouldn’t go with them. Although it seems they got a lot better compared to their chipsets from a few years ago, I just had too many bad experiences with them to really trust them.
Oh and if you decide to go Intel… I’d recommend Intel chipsets, they are really good. The NVidia ones are nice too, but when it comes to stability, they can’t beat the Intel ones.