Mountain Lion and Windows 8 can live happily on one machine. There are two ways to get Win 8 running on a Mac.
To run Windows from startup, you’ll need to install a bootable version of the OS using Apple’s Boot Camp, a program that partitions the hard drive and gets your installation running (for the actual installation, you’ll need to insert either a USB drive or a DVD with the install media on it). When you open Boot Camp, choose to both download and install support software. After that, the program will run mostly on its own, pausing only to ask how large you’d like the Windows partition to be. If you’re using the 64-bit version of Windows, give it at least 25 gigabytes. (You can always delete the partition later.)
You can also run Windows as a virtual machine—a fully functioning independent OS within another OS—with virtualization software. Parallels ($80) is a good choice, but as with any virtualization program, it’s not as fast as running Windows natively from a bootable partition. To get that kind of performance, plus the flexibility of virtualization, you can double up Boot Camp and Parallels. First, install Windows 8 via Boot Camp, thereby creating a separate partition. Then, choose the option in Parallels to treat the Boot Camp partition as a virtual machine. That way you can run a speedy Windows 8 whenever you want, without restarting first. No matter which method you choose, using Windows 8 on your Mac will be inherently finicky, especially because it relies so heavily on gestures. Hot corners on your Mac may override Windows when you’re in virtualization software, for instance, and getting your bootable Windows to accept right clicks on trackpads requires special drivers. You’ll get most of this support software with any up-to-date Boot Camp, and it’s also available on Apple’s website.