I personally wouldn't go with the Ailenware X51. It is unfortunately selling it's name more than anything else (for example, the one you linked is basically a low end, general use computer in a gaming computer's case). If you must go with dell then I would go with the XPS 8500 special edition because it has the GTX 660 as an option for a graphics card unlike the regular XPS 8500 without costing way too much for what you're getting like the ailenwares. However, I do not recommend a company like dell, hp, etc... for reasons that you would find out later.
Otherwise you could get something from a company like ibuypower, cyberpower, etc... (There are a good number of them out there). However, I would still highly recommend building your own computer. You will not only save tons of money, but you will learn a LOT about computers and it will be a beneficial experience all together.
If you are still reluctant, then watch the entirety of the first 2 videos here
http://www.youtube.com/watch?list=PL291F...PIXAtNGGCw. They are extremely helpful, and were how I learned how to build a computer. Before these I thought a computer was just a big magic box of electricity.