that looks like a good price for the alienware...
If I had a $2,000 budget I'd be building my own. But, that looks pretty good compared to some systems I just looked at.
Dell does sell some of it's systems w\ similar specs, but different case for alot less. You can get one of the "lower end" i7 920 systems for $700 and up...same specs 920,6gb,750gb, different case though... i'm taking my hat off to dell though, for the system you listed. The 5870 is listed as +$330 for upgrade, and the cheapest 5870 newegg has is closer to $400.
of course, a cheaper dell system would likely need a new power supply to handle a big card like that.