Like porksmash I got a new laptop a couple of weeks ago which came with Vista Business. Although I primarily wanted XP on it I thought it would be useful to keep Vista on it as well so I could play with it in the future.
I went through a long, involved process to dual boot Vista and XP, but I couldn’t get it working and, at 1 am and needing the laptop next day, I vaped it and installed XP alone. I did notice that Vista used 850MB sitting at the desktop with nothing very much running 
One thing you should be careful of when buying a current laptop with the aim of putting XP on it is the manufacturer’s driver support. Fortunately enough people had complained to HP about the laptop I had and they had drivers for all of the hardware. Some other manufacturers (such as Sony I believe) are not releasing XP drivers for their more recent kit.
To answer Nathan’s query about Linux, I’ve dabbled with it and like the idea of a completely open OS, but I’m put off by the lack of standardisation and difficulty of developing apps for it (although I guess knowing Java would help with that).