First off, as most of you probably know. This game is being ported from the 360 to the PC, as multiplat games tend to be very easy to run( designed for what is becoming very old hardware after all) You really don't need $1000+ machines to max the game, let alone run it decently. Just this last winter, built my brother a budget PC for gaming, $540 total cost, and that's with $100 for Windows 7, and it devours everything we have thrown at it.
For a quick rundown on CPUs, from worst to Best, it goes something like this.
Phenom |more or less equal| Weaker Core 2 Duo > Athlon II X2 > Good Core 2 Duo > Athlon II X3 > Athlon II X4 > Phenom II X3 > (slightly) Weaker Core 2 Quads > Weaker Phenom II X4 > Good Core 2 Quads > Good Phenom II X4 | more or Less Equal| first gen i5, and weaker first gen i7(i5 560, i7 760etc) > Sandy Bridge ( i5 2500, i7 2600 etc)
That's it more or less. Dual Core will get you by for now, but not for too much longer. You should be able to play Skyrim, maybe even max, with one, but not if you plan on listening to music, IMing, etc in the background. And some people mentioned Battlefield, BC2 is one of the few games that not only utilizing quad cores, but Hexas as well, it will eat everything you can throw at it. BF3 should be the same. (The ability to max Skyrim, and the ability to max BF3 are very different, requirement wise, they are in different leagues)
just for bare minimum, a Athlon II X2 or a Core 2 Duo should be fine to simply play. If you have at least a Athlon II X4 or a Core 2 Quad, you're set. Even those older CPUs, are more than adequate for a market full of console ports.
For GPUs, since that is even more complicated. I'll simply say that for AMD ATI cards, be in 4000 , 5000, or 6000 series. as long as the second digit is a 6 or higher, you should be fine, ie 4670, 5670, 6670, you should be fine. if the second digit is a 7 or higher, your more than set, unless your playing at above 1080P. X8XX and up is overkill. For Nvidia, it's much the same, they just have 3 digits for their cards instead of 4. so instead of a 4570, it'd be a 450 for example. for Nvidia cards, a 450/550ti and up is what I'd recommend. If your building a computer from scratch here, and trying to as cheap as possible a 5770/6770 should be around $100, a 6790( my personal best bang for your buck sub $150 card) and a 460, shouldn't be too much higher. Anything above is really unneeded for this specific game. People with stuff like a 5450, and 450 etc, are really the ones that should look at upgrading. You lucky guys with 6950s and the like, your set for this game, and likely for the next FO or TES game( probably max it at that) which ever comes first.
I could help with people asking about upgrade individually if anyone is not sure. or those asking about the "ti" on some cards like the 560 ti, it is indeed very different from a 560. Basically, the ones with ti, are a lot more powerful than the ones without, and consequently, need more power, and cost a bit more.
Hope this helps