Well, if you are handy and are comfortable building your own, you should be able to get everything you are looking for for about that price a
www.newegg.com . I have bought a lot of stuff through there and their prices are good, they ship fast and I have only had to send one thing back and it was no problem. Considering I have put about 8 computers together from parts bought there, one bad part is not bad. I have had worse luck buying retail and have had to pay more.
As far as what to get... you pretty muck know what you want. If you go that route, make sure you visit the manufacturers links and read into it and buy compatable stuff for what you want. Regardless of where or how you buy, I suggest going with name brands, they have the least problems in the long run.
I am highly partial to ASUS motherboards and have used them exclusively on the last 5 that I have built. If you buy nothing else in a "retail" box, get your motherboard that way, though you can sometimes find documentation for OEM boards from manufacturer sites. You can save some $$$ buying OEM components, but be aware that they do not come with any accessories and documentation. Some components may require additional parts (CPUs for intance will need thermal gel, heatsink and fan).
I strongly do not recommend buying a computer from any retail outlet. Speaking from first hand experience, they milk you on price and do not care what you want. A lot of times, stores have a marking system that you can sometimes spot that let the salespeople know what models have push priority and have commission bonuses for the sales guys. THey will do most anything to convince you to buy what will make them money, not will make you happy. The end result is Less computer for more $$$
Dell and Gateway (Dell being the better of the two) are OK, but usually cost almost DOUBLE for what you could build yourself. Be very cautious of the "el cheapo" specials they advertise on TV and on their site. These are typically very substandard computers and do fine for the average housewife who wants nothing more to do than hang out in chat rooms looking for people to leave their husbands for, but are not ideal for people like you and me, who like playing games or running high-end applications. They also typically have limited upgrade potential so when you are ready to do that, you sometimes get stuck.
So there is my quick 5 minute new-computer tutorial. I just upgraded 2 of my computers at home, including installing a Plextor 716SA DVD burner (SATA interface) and a few other luxury goodies. My secondary work station is now my home made DVR and has DirectTV plugged in. It also connects to my home theater amp so I can blast my music collection over the house. Fun stuff.