I'm now happily using an HP ProBook 4710s (2.1GHz core duo, 2GB RAM, XP Pro) which is a great improvement over my last machine - but then it would be. I'm too embarrassed to post the specs of its predecessor. :)

The only thing I would change if I could is the display - at 1600 x 900, it has plenty of pixels, but a 4:3 screen or even a portrait monitor would be better for much of what I do. Widescreen is good for music and audio editing, which tends to work horizontally, and for watching videos (which I hardly ever do anyway); but for documents and for Poser work with standing figures, it's limiting.