For around that price, I'd avoid Dell, but possibly think about Toshiba. I used to work for them, and even as an ex-employee I will say that I found them very sturdy, reliable machines, even at low-end. Some models even come with an option between XP, Vista and Ubuntu. I would seriously have a look at what they have to offer at the moment.
Don't have much experience with other laptops really, oh apart from Sony Vaio. When you strip all the pre-installed Sony cr@pola off them, they can also be very sturdy and reliable. Unfortunately, I think with Sony you might pay through the nose for the name, but they are fairly good, nonetheless.
I remember hearing some good things about Acer a while back, and I am given the impression that if you're on a budget, they can perform quite well and have a fair spec for that price.
My advice would be to go on to any independent review site and see what their customers have to say about each of the makes named above. Always good to do a little research with the owners, as they are normally the most scrutinous of critics.