Here's the deal, unless you travel a lot or room is a commodity in your house, there is no reason at all to own a laptop. There is no comparison between a laptop and desktop, the desktop will always outperform a laptop on a bang-for-buck scale.
The build Ksarex has there is solid, I'd personally change the CPU cooler (The Hyper 212 EVO is popular and effective though) to a CM V6 GT (which performs only slightly better than the 212 but looks a whole lot nicer IMO) Perhaps change the case to one a little nicer like the Rosewill Patriot which has a window (I have one, it's quite nice)
That's really all I got, forget the Alienware, they do have some desktops but they don't come cheap