Hint: DONT BUY FRIGGING ALIENWARE.
First you want a nice cpu. I recommend intel i5 2500k because it has oomph and isn't silly expensive. I personally use phenom ii x4 but it is just enough for my needs.
Second skyrim doesn't use a lot of video card ram (how I know this?: I got ridiculous resolution, fxaa and 2k textures and maybe 2fps drop compared to vanilla) so want to focuse of videocards with horsepower and not vram (ie 560gtx ti is nice, I have 6990 hence my silly resolution)
Third. How large is your TV's/monitor's resolution? What mods you want to try? What is your budget (I'm assuming you are super rich as you were considering alienware)?