(A) i heard alieanwear isnt that good. (cus u really need the fastest CPU you can buy overclocked?)
(B) go on irc and ask people there.
(C) my own personal experience now (which many people will disagree with but there we go)
I got a new pc (a few weeks ago) before i brought anything i asked on irc, and about 6 people from various stores to get a computer which can run games (i can run gta:iv on higest levels and it still doesnt eat up my cpu nor gfx card ram)
So i would suggest you do the same.
A great tip (which someone gave me) was to do this "buy a good "Family pc" (one with the cpu, ram, os and HD you want) for X amount. Buy a good PSU, GFX card and Case - and you have a nice computer.
Also, be aware of CPU's - speed isnt a massive issue any more - L3 and L2 caches are better - more MB on L3/L2 the better the CPU.
CPU's - remember if you go for intel - i7/i5 can both be quad or duel core. AMD are slightly easier X2 - duel, X4 = quad X6 = Hex,
Hmmm what else - Nvidia release the 500 series in a month (or so ive been told) and the 470 is fantastic (except heat issues) so i would suggest a 470/480 or a 500 series (i belive the 470gtx is the cheapest out of them, but its plenty powerful)
Try to get 64X OS (win 7 64) with a cpu which can handle 64bit applications and then get about 6gb ram. Try to get DDR3 Ram as its the newest and fastest.
Hard drives - try to get a decent one with good speeds (ask someone else on this lol)
If you are going to play lots of games, get a big HD (at least 500gb).
PSU - get a good psu, and i would suggest if you need 550W to power gfx card/mobo get about 600-650W for extra power, in case u want to add more later on, or upgrade.
Do not skimp on price. I did once, came back and bit me on the ass. So on this computer i did not. I tried to get as much as i could for my money.
hmmm...i think that is all. IMO DO NOT buy a "gamers pc". I actually got my computer, which is BETTER than a "gamer pc" the store was selling, for 300£ less. And the gfx card and case are better!!
Do not do what i have seen people do "buy two "good" gfx cards and use sli. It wont prodcue as much dedicated video ram as one great gfx card. Go over board on things, and you will be much happier.
Now if you really want i can post the specs of my pc, as i can run gta:iv on max, nfs:hp, and a few other games (i do not play many games atm...waiting for some to come out!)
Other than that as i say use IRC (dugi/carol/benny are good at this, esp dugi and cpus!)
Ask in store, and ummm....i think that is all.