1. Not Alienware! Build you own.
2. Well there is a couple of stickies to read ;)
3.
This should get you started.
Firstly, $3000 is WAY too fucking much. Ok?
$600-650 will get you a computer that can play anything.
<$1000 will get you a computer that can play anything on extremely high / max.
I would suggest;
an i5x4 CPU (sandy bridge if you want)
4gb of RAM (upgrade to 8 if you want)
1TB HDD + 64GB SSD (upgrade the HDD if you want but the SSD should be only 64 at max, total cost should be around $80 + $80 = $160 for both)
560 Ti OR 6950 GPU (the 560 Ti could be upgraded to a 570 but the price jump is $100)
Go for a 650W PSU.
Look at the guide. You
should be looking at Great - Excellent.
That should be fine.
Use the rest of the money to buy upgrades after every year so you stay in tip-top shape.
No need to drop $3k on something that will be worth $500 in a year and a half...