If you want to use Vista as your main operating system, we'd suggest buying a PC -- it will be much cheaper.
There are two ways to run Boot Camp (a free download from Apple) to install Vista on a separate partition to . The second is to install Parallels Desktop for Mac (US$49), which is virtualisation software which emulates Windows Vista under Mac OS X.on a Mac. The first is a dual-boot scenario using
I use a MacBook Pro at work and use Mac OS X as my primary operating system. I only load up Vista under Parallels to test our site in Internet Explorer -- it's more convenient than rebooting every time into Vista (the Boot Camp option). You don't want to run it full time in Parallels as it takes up so much memory. It also takes a while to boot up the operating system in Parallels under OS X to run a single application such as IE. There is a maximum amount of memory you can assign for Vista in Parallels, too: 1.5GB of RAM, 32MB graphics memory -- not enough to get the pretty Aero effects and certainly not enough for serious gaming/DirectX apps.
Boot Camp, on the other hand, is not virtualisation software: you choose at startup which operating system to run by holding down the option key (and you have to assign one as the default when installing Vista). Apple doesn't officially support Boot Camp or Windows at this stage (the software is still in beta), nor does it sell Vista with its Macs. Also, not all of the Mac components -- remote control, motion sensor, light sensor -- work under Vista because of driver problems.
No matter if you use Parallels or Boot Camp you'll need to factor in the cost of Vista ($385-$751) as a separate purchase for a Mac.