Alienware is just a brand name, if you put the same hardware in a Dell it won't preform any less.
When I think PC's only a few names come to mind. Alienware (expensive), Dell and HP (cheaper). Before, when I was a noob, I used to think of Alienware as strictly high end and for gaming while Dell and HP were for everyone else, but really as long as the hardware is in there it doesn't matter the name.
Another seller you may want to consider that caters to gamers is Falcon Northwest. I have never owned one of their products and they seem to cost as much as Alienwares, however they have very cool case designs to choose from if you're interested in that.
www.falcon-nw.com
Lastly, building your own PC is the best way in my opinion. It's much cheaper, you learn a lot and there's nothing like installing a fresh clean copy of Windows on it without all that added BS from one of the manufacturers.
EDIT:
I don't remember if I used I guide when I built my PC (first one) a few years ago. Really there's just a list of components your need.
- Motherboard
- Processor
- Video card
- RAM
- Audio card (optional, I threw mine out)
- Hard drive
- Power supply
- Case
Start with a well reviewed motherboard and build from there. I used NewEgg.com for everything I bought. You can search for the best products and easily see the detailed specs. The biggest thing you'll have to pay attention to is what the motherboard is capable of handling. Meaning what types of video card sockets does it have, what type of connections for hard drives, how many slots for RAM, and most importantly is the socket for the CPU compatible with the one you've chosen.
Just make sure each component works with the mobo, your power supply is strong enough, and you've chosen a good case to build in and you should be on your way.
Most computers are in mid-towers, but if you're nervous like I was with building my first check out the full towers. They offer a lot more room to move around in.
Good luck.