Three Monkeys, Three Typewriters, Two Days

More on laptops

One other constraint: I'd like the thing to run as cool as possible....

Looking for a laptop (and advice)

So I've finally decided to break down and get a laptop. My main criteria are as follows:

• Useful Unix-like operating system with X. In practice, that means I need to be able to run Linux or MacOS X on this machine.
• 15 inch monitor.
• Good battery life.
• Light weight (insofar as it doesn't conflict with battery life?)
• Preferably being able to get it here and all set up before June 24.
• Something either somewhat extensible (as far as laptops go) or that won't become too obsolete for several (3-4?) years.

Now the thing is that I've never bought a laptop, or used one much, and I haven't bought any computer at all in about 5 years. So I'm trying to catch up on what the market looks like, etc, and if people have any advice I'd much appreciated. If you know of places in the Chicago area where I could go and look at actual physical laptops, other than the Apple store, that would be lovely too.