HELP BUYING NEW GRAPHIC AND AOTHER.

Hello after beeing a little bussy with my life, I come back to the forum, speacially to ask Mugen some things.
Ok im about to buy a new graphic card, new fan, new powersupply, maybe a case, and maybe new processor . So here are my questions for everybody no matter who you are you can answer. I dont know about computer at all, but I've been learning from youtube and google so I need help.
Questions number one: How do I indentify a good graphic card? What are the features i have to look for?
Question number two: What is the fan for? the processor? the simply bentilation? or what?
Question number three: Do the case has to be very open? I mean with lots of holes around?
Question number four: the power supply can be around 600 or 700 watts?
and that's all if something comes to my mind I will ask, im sorry about this but I really need help.
Is my processor powerfull enough for a good graphic with DDR5, 1Gb, directX 11 and can I install a Nvidia with an AMD processor?
I calculated the price for everything except case and processor with compusa and it cost me a little less than $300
Information about my pc:
Processor: AMD Athlon ll 250
Ram: 5 Gb
Powersupply:(i dont remember) it was between 240 and 260watts
If someone needs any informatio please feel free to ask me.
Mugen I never had a graphic card it was a integrated graphic card.

Hm, how do you choose and identify good things - expirience, test-reviews, consumer feedback.

I check hardware sites from time to time, read tests to new graphic cards and cpus: performance, needed power, noise, cooling and price - that all has to fit.

Same goes for CPU-fans, price and cooling must fit. But the CPU has to be based on a good motherboard, either it's a fail, cheap shit will decrease the overall performance.

The case should have enough space avaiable for at least 3 case-fans (even though with 120mm usually 2 are fine), enough space for graphics cards to not suck their own heat, enough space for a good cpu cooler (ofc that depends as well of the motherboard layout), the power supply must be placed at the very bottom (anything else is bullshit and leads to decreased power supply lifetime).
Well it's hard to tell, I usually look at a case, at its core and outside and know if it's good or not, some work with full closed and excellent air flow, some work with grid cases.

The power supply depends on your hardware, usually the graphic cards needs the most, nowadays until 2x8-pin but many companies have calculators for that, people can use.

You can run NVidia and AMD together, though AMD CPUs suck badass (the very latest, Bulldozer shit - Phenom II was still OK), worse performance, worse cooling, worse volume, worse energy saving - but cheaper.

Your CPU is getting ancient mate, dual-core is about to die, programs now benefit form quad-cores more and more.

Anyway I cannot tell you further details if you do not tell me what kind of settings you are going to run, latest pc games at HD with mid-high settings will not run smooth at your CPU, this I can tell already. Your CPU is the stopper in your system, if you have same ancient motherboard forget about new good parts to place in, well I guess cards until GeForce GTX 460 768MB could run even better when you overclock your CPU to 3,5GHz (ofc you need a good CPU cooler and airflow), but every card above will suffer.

I can give you an example of an all-arounder from last year:
CPU: Intel i5 2500K
MB: GigaByte GA-Z68AP-D3
CPU-Cooler: Scythe Mugen 2 / EKL Alpenföhn Groß Clockner / Arctic Freezer 13
GRACA: Gigybyte GeForce GTX 560 Ti - OC / MSI N560GTX-Ti Twin Frozr II/OC
RAM: Kingston / G.Skill Ripjaws / Corsair DDR3-1300 2x4GB
Case: Xigmatek Midgard II
Power: Thermaltake / be quiet! (both with CMS) 550-600W (80-85+)

Well, to be honest, when I bought my new PC some years ago I was not patient enough to wait for i5 2500K instead I got this one:
CPU: AMD Phenom II X4 965BE
MB: Asus MA87TD/USB3 (very bad choice, but the bundle was so cheap . . .)
CPU-Cooler: Arctic Cooling Freezer XTREME Rev2 (the Freezer 13 was released much later)
GRACA: Sapphire Radeon HD 6850 Toxic (well, the GTX 560 came later, the GTX 460 would've been fine too but I usually go Intel/NVidia AMD/AMD because of drivers)
RAM: Kingston HyperX DDR3-1333 CL7
Case: Xigmatek Midgard
Power: beQuiet! Straight Power 580W CMS

And ofcourse: an SSD is the way to go nowadays, at least 60/64 GB for Windows, you will never want something else hahaha.

Well the two stated computers are the best example to say this: If I would have waited half a year more, I could have got a better PC for the same price ^__^
But still: Both configurations will work well the next 4 years, maybe not anymore with ultra settings but I don't care - still many games are converted from consoles which will reach the next level end 2013, beginning 2014 with slightly better configuration than the above ones . . . less games are nowadays made for PC (even TES went to consoles)

So... After hearing all these i got a conclusion.... A NEW COMPUTER... im gonna try to sell mine aleast get 500 box and that's it. Cuz buying all that new will be a waist of money and time ill try to buy a gaming computer even a ALIENWARE desktop ofcourse i dont want laptop i dont need it. And a Alienware would be a good choice??

Pal, if you shit money then buy Alienware otherwise keep your hands off.
I still wonder why people waste their money on it, it's not worth the price. A gaming-computer that will run the next 5 years must not cost more than one thousand bucks.

btw I dunno about the rest of your specs but you want to try to get 500 for it? Jesus I get a better cpu with 4GB DDR 3 ram, 500GB HDD and OK motherboard for 200€ here ;D

question: is it good to buy a new alienware for 900 to 1000 dollars?
cuz if you think so I would.
And its easy to sell a computer to people who only use it onyl for facebook... dont you think?
there's a lot of people who barely know how to turn on a computer so they wont mine about having a slow Cpu and a computer without a graphic card xD.
LOL

Hey Mugen I've seen that you know about a stoer named CompUSA.
Could you tell me a good computer I can buy for less than $1000.
please with good things you know, you are the one who knows about computers xD.
Or its better and cheap to build my own one?

I don't get your first sentence and I can only tell you the parts for a computer, not a complete computer as a) I don't know about any other than german shops and b) Own built are cheaper than complete ones.

Ok, could you tell me all the parts that a gaming computer needs from the case till the last screw, not above $1000, the less expensive the better for me. thank you very much, and im sorry for making you waist your time.

Yeah I can do that, but not very soon, within the week now, have more important things I have to care about currently

Ok I'll wait, just give the parts I need to buy to get a good gaming and high perfomance computer and that's it.