As far as the hardware goes, one major brand is really not all that different from another major brand, because they pretty much all use the same hardware. I think what separates one major brand from another the most is the product build quality and product support. Read up on reviews that address those issues. It's why I chose Canon.
As far as features go, I agree with the opinion that you'd want a 64-bit processor, preferably an Intel, IMHO. You will also want more memory and hard drive capacity than what comes with most basic PC packages. Most starter packages offer just 4GB of memory. To process photos efficiently, you don't want no less than 8GB.
I'd say that you'd want at least I TB of storage on your hard drive, preferrably with the addition of a mulit-TB archival storage for you photos. There are some very economically priced, multi-TB network storage devices. I use Western Digital network storage, and tend to shy away from relying on USB storage devices for achival use.
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