If you are going to have 4+ GB of RAM then you'll need a 64 bit operating system to address all of it. The thing that influences Dominions the most is raw computing power, so the CPU is the only thing of interest there, except maybe the graphics card, but anything you buy should work. As far as other resources are concerned, there are limitations in the game that make it run on hardware that is a couple of years old and those will be the same for your brand-new system. I wouldn't necessarily buy from Alienware because you pay a big chunk of money for the brand only, but if you have the cash and don't care... I've recently acquired a
HP Compaq Presario CQ71-205SG notebook with 4GB RAM, 17" HD+ screen and a Dualcore 2x 2,0 GHz CPU for just 488€.