I've talked to a few people who have used alienware and are happy w/ the performance and support from a windoze standpoint. But unfortunately alienware doesn't offer linux support which is ok.
I wouldn't use Dell even if someone gave it to me for free
IBM - In a heart beat but lack of ATI linux driver support has made me unhappy.
HP - Same issue when it comes to ATI.
Next choice, Alienware, they should thank nvidia for that
I'm open suggestions.