The MacBook is just over 5 lbs. and can run XP natively.

The reason I bring it up is that so many laptops are flimsily manufactured, IMO, and the Apples are not. As far as native Windows laptops, I couldn't recommend, based on build quality, much outside HP, Sony, Toshiba and IBM/Lenovo (assuming, as Dan says, that Lenovo hasn't done a hatchet job on build quality). And I have other qualms about each of those, too.