With all of the so-called "Enhancements" of XP turned off, I can neatly run XP on a 600Mhz computer. Although it seriously needs all of my 128Mb of ram, it still runs.
Now Vista requires (if I recall correctly) 1.3GHz. Since that particular computer is outdated, I cannot add another CPU. So on top of about $700 to $1000 for the Operating System, I'd need to spend an absolute minimum of $200 for a motherboard-CPU combo (according to anyone who knows me, I'd definately spend more then that, actually.). NOt only that, But I'd need to spend another $400 on the peripherals that were embeded on the first Mainboard. That's already around $1500!
Vista is already cr{bleep}.