From Mac Guides
Windows can be run in emulation on PPC based Macs using emulation software such as Virtual PC, and can be booted natively on Intel based Macs using Boot Camp or software available from http://onmac.net/.
The most current version is called "Windows Vista", and is based on Windows NT. The name of the kernel is NT 6, as Windows XP was NT 5.1. However, it has received much media attention because of its similarities to Mac OS X, and its high system requirements.