Parallels makes software for Mac computers that allows you to install Windows and run Windows apps from OS X without rebooting. The latest version of Parallels adds experimental support for Windows 8.
Microsoft released developer preview of Windows 8 recently. It features a dramatically redesigned start menu and new “Metro style” applications with a full-screen view and touch-friendly user interface.
Parallels Desktop build 7.0.14924 also offers improved copatibility with Quicken 2011, better support for AutoDesk 3ds Max 2012, and CPU usage improvements.
You can probably also install Windows 8 on a Mac using the built-in Boot Camp feature, but that would require you to reboot your computer every time you want to switch between OS X and Windows.