You most certainly don't. Even if you were building a high-end gaming rig (which your GeForce 570+ suggests), you'd be better off with more RAM and an SSD than a 2 TB HDD. There are also plenty of good non-Cosair brand PSUs. There are many i5s, including i5s from a generation ago, not a specific target at all.
Err.mm nope. You don't need more than 4 GB RAM, personal desktop won't go that far. I don't expect him to pull out 20 Photoshop projects and rendering animations at the same time. You can open 30 office documents at the same time and running some videos with a mid game running in the background in 4GB RAM. It is more than enough for daily consumer usage. Of course the RAM is rather cheap today, you can easily dash out extra cash for the extra RAM, just telling you most of it will be idle.
SSD is overrated IMO. Current HDD are already fast enough to handle heaviest tasks without hiccup. Writing with SSD is slower than writing on HDD, so he would need a big HDD as data/game storage, with SSD OS runtime, but this setup is probably too complicated for him. Besides, unlike console games, you don't call up the HDD everytime you change screen, so transfer rate is least of his concern. Games these days render contents through video cards on the fly, so as long as his card is good, there is little chance HD transfer rate would affect his enjoyment.
He can always research for good AMD chips and non-Cosair PSUs, but again, for a non-techie he has to dip his head with loads of new terms and then he would end up listening to the Alienware salesman instead. Nevertheless, I've tried 4 brands of PSUs and Corsair gives the best stable voltage amongst other craps I got.
The OP will also need:
-A case
-A motherboard
-A Windows Installation Disc
-A disc drive
So basically: Budget first, parts second.
He's not going to build it piece by piece. let the computer store worry about that for him. Since he's considering Alienware I suppose his budget is pretty loose, I'm just trying to help out so he could save more and spend on game titles instead.