You're kidding me, Gateway... LOL, no way in hell.
Alright, I suggest building your own, it's cheaper, it's convenient, and if you buy that Dell, you'll regret it. I'm a kind of guy that would like to know what I'm dealing with.
Anyways, I'm guessing you want to play some of these next gen games, Crysis, Aion, WoW, whatever..
Let me start off with the case. You're going to see smaller cases, which are called Mid Tower, and big cases called Full Towers. If you want this PC to be a gaming PC, you will absolutely need a Full Tower, just because, nowadays the video cards are big and bulky, sometimes even take up to two PCI-E slots depending on your motherboard.
Anyways, I would suggest this full-tower case:
http://www.newegg.com/Product/Product.as...-_-Product
As if right now, it's $160.00 and free shipping.
Secondly, a motherboard. I'm going to suggest a DDR3 RAM compatible motherboard just because in the future, you won't get passed up by older generations. Also, this one I am going to suggest is Tri-SLI classified motherboard, meaning that you can run three graphics cards (if you're that hardcore) at the same time. However, with that budget, you can't do that, but it's always good to know that you can upgrade from 1 card to 2 or 3.
Here is what I suggest:
http://www.newegg.com/Product/Product.as...-_-Product
Surprisingly, the price of this motherboard was static, but recently it went down $15 and it's free shipping, also, mail-in rebate.
Next in list would be a power supply (PSU). Seeing if this is just going to be a gaming rig with nothing to vital taking up power, I would suggest a 750 Watt power supply, that is more than enough if you're going to stay with 1 video card.
Here's what I suggest:
http://www.newegg.com/Product/Product.as...6817139006
$110, free shipping, mail-in rebate.
Alright, the most important would be the CPU. This CPU is 64-Bit compatible, which makes 6+ GB RAM easy to deal with. This is one of the newest series released by Intel, an i7 920. It runs at quad core 2.66 ghz but can easily be OverClocked to 3.4+ ghz.
Here's what I suggest:
http://www.newegg.com/Product/Product.as...-_-Product
$280, free shipping. Dropped $20 recently.
Now, if you're serious about this build, you're going to need some serious cooling for the CPU. I usually run around with 35 degrees C under no stress with my CPU Fan. If I knew how to deal with water cooling, I would definitely tell you exactly what to get, but I use air cooling. Definitely look into water cooling if you can.
For Air Cooling, I would suggest:
http://www.newegg.com/Product/Product.as...k%20knight
$45, free shipping. For some reason it went up in price recently.
Obviously, if you're going to play games, you're going to need a pretty nice video card. I highly suggest this with your budget, it's top of the line:
http://www.newegg.com/Product/Product.as...6814130433
$200.00, $30.00 mail-in rebate. This went down in price by at least $20.
You're going to need some RAM, obviously.. But the more the better, with that mobo (which can hold up to 12 GB) and CPU, I would suggest these:
http://www.newegg.com/Product/Product.as...6820231225
$135.00.
For a Hard Drive Disk, I would suggest something relatively large, something between 500 GB and 1 TB.
This is what I suggest:
http://www.newegg.com/Product/Product.as...6822136284
$95, however, it's SOLD OUT. :-( I would bookmark that link and wait when it's back in stock.
You're going to need thermal paste. This is mandatory and highly recommended. The stock thermal paste you get that comes with the CPU just sucks.
I would suggest this:
http://www.newegg.com/Product/Product.as...6835100007
$7 and it's re usable probably at least 5 times.
If you want to buy this case with this motherboard, you're going to need an 8 Pin Power extension, otherwise, it will be a tight fit and barley reach. I highly suggest it.
You're going to need this:
http://www.newegg.com/Product/Product.as...-_-Product
$8
Yeah yeah, I know.. This is over your budget but see what you can do!