Alienware are like Lamborghini's.... sold for way more then it worth, but it still a very nice PC, the best PC's IMO you can buy pre-built. I think you will love it, but alienware tech/warranty department... a nightmare to deal with...but other then that you will be blazing through everything you do.
I have a I7 930 with 6go ddr3 @1600mhz and hd5830 1go gfx card.. Built it end of 2010 and it still runs like a chief most of games with pretty much all graphics to the max without lag, depends on which games and I run windows 7 64 bits. My graphic card is getting a bit outdated but I don't play games anymore like I used to so it is really enought for me for now. Recently installed a 128go SSD drive to run as main HDD, and god it makes a real nice difference.
You should really like your new pc.. I agree with the others alienware are overpriced, but their cases look like they have excellent cooling for gamer pc.. It's better to just buy every part and build it yourself, you save a LOT of money.