I'd go for the Alienware (though i've not seen a VoodooPC).
...Just based on the videocards. I don't know much compared to most of you chaps (I'm getting bored of saying that but don't want to get technically slaughtered if what i say is stupid) but a 7800GTX doesn't seem that much compared to those Quaddro things in SLi, i'm probably completely wrong.
Sorry to be stupid, but...How is a GPU designed more for one application than another? Is it down to how much and how fast the memory on the card in and how fast the processor is...I mean, isn't 'more' just better for whatever you want?