Claudia:

I agree with Ray and Masaki, if you want powerful lightweight portability, I would stay away from Dell (way too heavy) and go towards Sony or my favorite, the ThinkPads. My ThinkPad ways only a little over 3 lbs and has been dropped, rolled a couple of hundred miles in my rolling briefcase, and generally mishandled without a problem. In fact, when my company said it was time for replacement, I decided to wait a while. If you are really hard on notebooks, I would look at Panasonic Toughbooks. We used them on an Air Force project for flightline maintainers because they were so sturdy while still relatively lightweight.

As for performance, you can get enough memory, speed, and disk space on any machine. After all, all the parts are "commodities." What you want is a great design for your needs. If you do go for a dell, try it out. Some of them have a bad battery design wherein you can burn your hand as battery is right where you rest your wrists.