I second the motion (MacBook). You can run both Mac OS X and Win XP SP 2. I have a Mac Mini (Intel) that is triple boot - OSX, Win XP and Linux (Fedora Core 6).
I plan on getting the MacBook sometime this Summer.
I got rid of my old Dell in favor of the Macbook. The thing is a pleasure to use, even though I’ve had to learn the “new” OS. I also love its compact size, for traveling.