My personal experience as a professional technician is that Alienware is the same garbage in a prettier package. They used to be a very high quality niche manufacturer before they got bought by Dell; Dell gutted them. If you buy Alienware you are buying a Dell with a goofy looking alien face slapped on the cover and an even more ridiculous price tag.
If you want a gaming machine that you can take around with you, don't buy a laptop anyway, get a small desktop PC, a flat panel monitor, some 3d surround headphones, and a nice case to carry them around in. You will always pay twice as much for half the machine if you insist on cramming high-performance hardware into a laptop size, and you'll get a really bigass unwieldy laptop in the bargain. Just don't do it. You can get (or build) a PC half the size of a normal tower in all dimensions (about the size of an xbox) and still get really good quality performance parts in it, a much better screen, and about the same portability as the gigantic slab of a gaming "laptop" you'll end up with.
Personal preference of course, but I know a lot of people who buy big gigantic laptops and either find they loathe to unhook them from their spot on the desk (shoulda bought a desktop) or find the thing is so big it's not practical to use in many situations (shoulda bought a small notebook and forgot about 1337 gaming power), or find the thing cost a fortune and didn't really deliver the promised performance (shoulda bought a desktop). You can't take it back, and it's a big chunk of money.
Try this, go buy or borrow a really big, really cheap briefcase, about 18x14x4, and put around 10 pounds of bricks in it, and carry that around for a month; sit with it on your lap in various tight places like airplane seats or folding chairs or tables in coffee shops and pretend you're typing on it; leave it out in the sun during the summer and let it get nice and hot, then plop it down on your legs (because the thing will get really fucking hot when you're playing a game). Oh yeah also bring a mouse and try to figure out where the hell you plan to put it while the laptop is on your lap and you're having a grand ol' time playing Crysis on the bus. If you find all these things quite tolerable for a long period of time in exchange for being able to play great games on the go, definitely buy that laptop. Otherwise, buy a nice small laptop and play games in ugly mode, or a gaming desktop and a DS/PSP :D