No, its not just about CPU power either. I was running an AMD 3600+ with vista which supersedes the minimum requirement. Today, it is really all about RAM. Especially with vista. Vista preloads everything into memory, and utilizes a lot of your RAM. Virtual machines take very little CPU usage, but require a chunk of dedicated RAM that only that virtual machine can use. CPU is definitely important, but it really just depends on what you are doing. You can have the most powerful CPU of all time, but if you only have 512mb of memory you won't be running vista that well at all regardless of how high end of a CPU you have.
Vista was meant to be a lot of things. Where is the EFI support? Eh? Where are all the new features? Really, the only benefit the end user gets from vista is a flashy new interface. Every other feature is geared towards IT/Tech people. There are more tools to find out why your system crashed than in any other OS in Vista. Microsoft just had the wrong approach. They tried to compete with how slick OS X looked, and how it utilized open GL, etc. Instead they should have been thinking about adding intuitive features to their OS to make it a better experience for the end user.
Look at Leopard...I just installed it this week on my Macbook Pro. I have had no crashes, and so far only one application of mine doesn't work. Casper Admin utility doesn't quite run right in Leopard. Look at the features they added for the end user. Space, multiple desktop support built into the OS for the productive user who does a lot at once. Time Machine - nearly 80% of users do not back up their data. Apple made a simple and intuitive way for people to back up their data to an AES 128bit encrypted sparse image file. So now maybe 50% of computer users may start backing up their data on regular basis, and that is a good thing. Spotlight, with quick search indexing. This allows users to instantly find things.
I am not saying Vista doesn't offer nice features, I am sure I could list all the nice new features you get, but they aren't taking the approach of adding intuitive new features for the end user. You also have to take into account your average user is your average user. They don't know how to write a cron job with rsync to automate back ups over a network, let alone even have a network. However, time machine is click, drop, and drag, so it is way easy for the user to back up their data.
I love it when people try to say mac users are dumb because of how simple the OS is. Really they are smarter, because it is more efficient, easy to use, and it just simply works. Also, under the hood is bonafied Unix. So you can do very advanced things from the command line. You can use robust scripting languages, and you can pick apart the contents of applications and adjust them to your needs. Trust me, OS X is way more advanced under the hood. Windows has been promising self contained apps for how long now? XP with SP 2 is solid. In fact I am typing this on my Xp machine as we speak. There is no benefit from running vista at all over XP because it doesn't offer any deal breaking feature, not even to the most advanced power user to your grandma who barely knows how to use email.