This year I ran a lab in which I was able to observe XP, Vista and GNU/Linux running on a variety of hardware:
1)Vista sucked on AMD64 X2 5000 with 2 gB RAM
2)XP was OK on P4 with 512 MB
3)GNU/Linux on thin clients with 64 MB was the best.
I should explain the last item. I ran 24 users on thin clients from an old XEON server with 2.4 gHz clock and 2 gB RAM, 80 MB per user on the server and 64 MB on the client=144 MB and 100 MHz per user on the system. This means Vista is many times less efficient than GNU/Linux. Vista may be designed to maximize profits for M$ and Intel but it sucks bigtime for the customer/user.
A recent server by KACE found that 11% of IT professionals were in the process of switching from M$ this year, more next year and a bunch after that. In two years the M$ monopoly will be down the drain, thanks to Vista and M$'s contempt for users. M$ could fool all of the people some of the time and some of the people all of the time but they cannot fool all of the people all of the time.
M$ should invest its billions re-inventing itself and not the OS. If they do not they will be a dinosaur within five years. Once the monopoly is broken, they will have to compete on price/performance and Vista-like OS will not make the cut. It's time to change to a UNIX-like OS be it MacOS, openSolaris, FreeBSD, or GNU/Linux. I recommend GNU/Linux because it has been doing the job for ten years or more, has fantastic (and still improving) device support, is modular and configurable, and is lean when you need it to run on anything built in the last ten years or more.
In 2006, I built a complete IT system for a school using GNU/Linux. They were able to afford twice as many seats plus toys for the price of a system running M$. M$ makes no sense to anyone who cares about price/performance and who is not locked in. Emerging markets are not locked-in and M$ will be irrelevant soon. Get used to it, Mike.