i have an alienware m9700, the base model, and it blows through every game i have thrown at it. I had it shipped with Windows MCE though b/c vista really isnt up to snuff yet. The 2gb option i think is 270 more, but its prolly cheaper to buy the mem you want online.
I dont think it has upgradeable videocards, but there really is no point to that, besdies if you wanna worry about the future, this notebook can have a SLI config, with two 7900's