While this is good advice many laptop manufacturers ridiculously overcharge for system memory (Dell is usually one of those). I recommend buying the laptop with a very good video card and as little memory as you can configure it with. Then go to Newegg.com and order a 2GB twin pack (I prefer Corsair ValueSelect, good price, lifetime warranty and their memory has always worked well for me). It's actually very very easy to install the ram yourself and you save a good bit. Feel free to PM me if you have any questions.

Edit: You may also want to take a look at the Killer Notebooks Kodachi. It's a 14.1" screen and weighs 5.4lbs, when configured with 2GB of ram and a 100GB 7200rpm hard drive it shows a price of $1799 with nearly the same specs as the XPS you posted. I couldn't find a review of this exact notebook in the few seconds I looked but Techware Labs has a review of one of their other notebooks and they speak highly of the company in it.

Edit 2: It also has a Nvidia GeForce 7600 w/ 256MB of video ram as opposed to the 7400 Turbo you have listed for the Dell