I will make this as short and as quick as possible, I am a die-hard Nintendo fan but I am open to play games on all consoles available (I own a PS3 and 360)

yet, after spending a great time this summer playing Skyrim on my PS3 I noticed that the PC version is just superior in everyway to add insult to injury I noticed that STEAM's summer sales were just out of this world, so I bought the Bethesda package and I downloaded Skyrim and threw a prayer that my old PC would run it, it did but lagged up to a point it just wasnt playable, so I decided to build my own Gaming PC!!!!!

I need to get some information since I am not an expert on identifying specs, to make things worse I have about $400 to invest in it,

so I will tell you what I already have......

1 ASUS GeForce GTX 560 TI PCI-E 1GB DDR5 Graphics Card

1 675 Watt Power Supply,

1 Raidmax Augusta Case

Operation system, Windows 7 Pro.

Ok, so I am totally lost with the whole Intel, I3 or I5 or I7 Dual or Quad Core, or the AMD and what motherboard to buy, and what else am I missing? please remember that i only have $400 dollars ( I have separated another $450 for the WiiU release) will it be enough to run Skyrim in Ultra setting? or should I return  what I have purchased and stick to Consoles?

so you have $400 to spend on a CPU, Mobo, RAM, HDD? Or $400 in total including the stuff you have?

I am going to assume that you already have Mouse & Keyboard and a Monitor/TV. 

I have a 560 Ti myself and it runs everything I throw at on high-max settings at 1080p with a smooth framerate usally arround 60fps. 

Something like:

http://www.newegg.com/Product/Product.aspx?Item=N82E16822148702
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231314
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130655
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115234

??

Bear in mind I don't have much experience with Intel so I don't know what the most fantastic chipsets etc are. However it ought to run anything this and next gen throws at it. 8GB RAM = why not? Also if you wanna blow another $100 on an SSD it'll be even better.

Since you already had a GTX 560 Ti the reason for your lag in Skyrim must have been something else rather than hardware (I just can't imagine you have a single core CPU or less than 2GB system RAM. No one has a modern GPU together with such old parts).

So try some software solutions first, like checking how other modern games run on your system and then perhaps re-install Skyrim and patch it.

It sounds like he's just bought that stuff.

--

How old is your 'old' PC? Have you tried putting the new GPU into it and seeing what framerate you get?

Other than that, Squillam's suggestions look good.

To answer all of you, I have $400 dollars plus what I already have, those parts I mentioned are still in their boxes, have not connected any of them, my current PC runs on an Intel Pentium G620, with a 3GB ram, BTW I plan to keep my Hard Drive, is that a good idea?,
BTW I do have a decent mouse Keyboard and Monitor

You will be stunned by how much graphical difference enb modding can make to skyrim on PC, not to mention a whole load of new content added by other mods. I have over 600+ new spells that scales with perks and spell power armors etc. I cringe whenever I see a buddy of mine playing vanilla skyrim on his xbox. 

http://imageshack.us/f/846/screenshot157n.png/
http://imageshack.us/f/7/screenshot174t.png/
http://imageshack.us/f/52/screenshot198a.png/
http://imageshack.us/f/641/screenshot224g.png/

http://imageshack.us/f/651/screenshot207pt.png/

Those are in-game graphics though some quality is lost in transition to screenshots.

You already have a decent GPU so grab a good processor, (look into intel i7 series) and overclock it. I have an intel core i7 930 2.8ghz overclocked to 4ghz with ATI radeon HD 5850 backed by 6gb of ram. Bought it over two years ago, can still handle anything I throw at it.

Whatever you do, seriously consider overclocking your CPU, that's the only way you get the most out of your bucks.

Don't do this, it's not necessary to run what you want to run, it increases power consumption proportionally more than the increased performance and it does void your warranty. In other words it's only worth doing if you know why you're doing it.

All >$150 Intel CPUs of today will run everything you would want fine for a number of years, and there is no such thing as future proofing in computers.

sandy bridge or ivy bridge i5 should do ya skyrim is quite cpu bound ... then a z77 motherboard ... OC only if you feel comfortable doing so, tomshardware is an excellent resource ... reviews from arstechnica, tomshardware hardocp & anandtech are all top notch for helping pick out parts.

for motherboards MSI has been good to me ..gigabyte okay.... ram get ddr3 1600 or better and at least 8gb but 16 would be better its dirt cheap right now.... i have 32 gb running in the vgz minecraft server

what case are you using?

edit : if you can swing the cash for it a 128gb ssd as a boot drive is amazing.. day and night difference  ... if not save that for your next upgrade 

Get the cheapest hard drive you can. It's the easiest thing to upgrade since you can buy external ones.
Put the most weight on the processor and RAM.