laptop for gaming

[michael0224]

Hi, I am thinking to get Dell Ispiration 9400 (dual 2.0 cpu, 1g ddr 667ram, 256 nvidia video card). How long do you think this can last me for 3D gaming until i will need a upgrade? I would like to go for their M1710 but that's like 1/2 more than I9400.
In terms of hardware, is a dual cpu or a 'very' fast single core cpu better for games?
And what other things I should look at?
Plus, I would like to leave it on overnight for downloadings just same as the desktop I had before. Does it harm the laptop if I give him a nice cooling? And can a laptop work without a battery? So that I could just connect it to the power straight.

Thanks.